diff --git a/Gopkg.lock b/Gopkg.lock
index 9ca4de6855..9c8b9f0ca3 100644
--- a/Gopkg.lock
+++ b/Gopkg.lock
@@ -11,13 +11,13 @@
   branch = "master"
   name = "github.com/btcsuite/btcd"
   packages = ["btcec"]
-  revision = "1432d294a5b055c297457c25434efbf13384cc46"
+  revision = "86fed781132ac890ee03e906e4ecd5d6fa180c64"
 
 [[projects]]
   branch = "master"
   name = "github.com/cosmos/bech32cosmos"
   packages = ["go"]
-  revision = "efca97cd8c0852c44d96dfdcc70565c306eddff0"
+  revision = "c12e4b6ed52acc1d35fea49acec35f980914dc95"
 
 [[projects]]
   name = "github.com/davecgh/go-spew"
@@ -256,7 +256,7 @@
     "leveldb/table",
     "leveldb/util"
   ]
-  revision = "e6d6b529196422703d54ff5c40e79809ec2020b3"
+  revision = "5d6fca44a948d2be89a9702de7717f0168403d3d"
 
 [[projects]]
   name = "github.com/tendermint/abci"
@@ -267,8 +267,8 @@
     "server",
     "types"
   ]
-  revision = "78a8905690ef54f9d57e3b2b0ee7ad3a04ef3f1f"
-  version = "v0.10.3"
+  revision = "f9dce537281ffba5d1e047e6729429f7e5fb90c9"
+  version = "v0.11.0-rc0"
 
 [[projects]]
   branch = "master"
@@ -298,17 +298,14 @@
   revision = "915416979bf70efa4bcbf1c6cd5d64c5fff9fc19"
   version = "v0.6.2"
 
-[[projects]]
-  name = "github.com/tendermint/go-wire"
-  packages = ["."]
-  revision = "fa721242b042ecd4c6ed1a934ee740db4f74e45c"
-  version = "v0.7.3"
-
 [[projects]]
   name = "github.com/tendermint/iavl"
-  packages = ["."]
-  revision = "fd37a0fa3a7454423233bc3d5ea828f38e0af787"
-  version = "v0.7.0"
+  packages = [
+    ".",
+    "sha256truncated"
+  ]
+  revision = "c9206995e8f948e99927f5084a88a7e94ca256da"
+  version = "v0.8.0-rc0"
 
 [[projects]]
   name = "github.com/tendermint/tendermint"
@@ -319,6 +316,9 @@
     "consensus",
     "consensus/types",
     "evidence",
+    "libs/events",
+    "libs/pubsub",
+    "libs/pubsub/query",
     "lite",
     "lite/client",
     "lite/errors",
@@ -347,8 +347,8 @@
     "types/priv_validator",
     "version"
   ]
-  revision = "018e096748bafe1d2d1e69b909e4158f3b26f6b2"
-  version = "v0.19.5-rc1"
+  revision = "73de99ecab464208f6ea3a96525f4e4b78425e61"
+  version = "v0.20.0-rc0"
 
 [[projects]]
   name = "github.com/tendermint/tmlibs"
@@ -361,12 +361,10 @@
     "db",
     "flowrate",
     "log",
-    "merkle",
-    "pubsub",
-    "pubsub/query"
+    "merkle"
   ]
-  revision = "cc5f287c4798ffe88c04d02df219ecb6932080fd"
-  version = "v0.8.3-rc0"
+  revision = "d970af87248a4e162590300dbb74e102183a417d"
+  version = "v0.8.3"
 
 [[projects]]
   branch = "master"
@@ -382,7 +380,7 @@
     "ripemd160",
     "salsa20/salsa"
   ]
-  revision = "1a580b3eff7814fc9b40602fd35256c63b50f491"
+  revision = "ab813273cd59e1333f7ae7bff5d027d4aadf528c"
 
 [[projects]]
   branch = "master"
@@ -396,13 +394,13 @@
     "internal/timeseries",
     "trace"
   ]
-  revision = "57065200b4b034a1c8ad54ff77069408c2218ae6"
+  revision = "1e491301e022f8f977054da4c2d852decd59571f"
 
 [[projects]]
   branch = "master"
   name = "golang.org/x/sys"
   packages = ["unix"]
-  revision = "7c87d13f8e835d2fb3a70a2912c811ed0c1d241b"
+  revision = "c11f84a56e43e20a78cee75a7c034031ecf57d1f"
 
 [[projects]]
   name = "golang.org/x/text"
@@ -463,6 +461,6 @@
 [solve-meta]
   analyzer-name = "dep"
   analyzer-version = 1
-  inputs-digest = "f0c6224dc5f30c1a7dea716d619665831ea0932b0eb9afc6ac897dbc459134fa"
+  inputs-digest = "a6a5d886519fa9ca97a23715faa852ee14ecb5337e03641d19ea3d3d1c392fee"
   solver-name = "gps-cdcl"
   solver-version = 1
diff --git a/Gopkg.toml b/Gopkg.toml
index a1adc79ac7..deabcd6452 100644
--- a/Gopkg.toml
+++ b/Gopkg.toml
@@ -54,43 +54,37 @@
 
 [[constraint]]
   name = "github.com/tendermint/abci"
-  version = "~0.10.3"
+  version = "0.11.0-rc0"
 
 [[constraint]]
   name = "github.com/tendermint/go-crypto"
   version = "~0.6.2"
 
-[[override]]
-  name = "github.com/tendermint/go-wire"
-  version = "0.7.3"
-
 [[constraint]]
   name = "github.com/tendermint/go-amino"
-  version = "~0.9.9"
+  version = "=0.9.9"
 
 [[constraint]]
   name = "github.com/tendermint/iavl"
-  version = "~0.7.0"
+  version = "0.8.0-rc0"
 
 [[constraint]]
   name = "github.com/tendermint/tendermint"
-  version = "0.19.5-rc1"
+  version = "0.20.0-rc0"
 
-[[override]]
+[[constraint]]
   name = "github.com/tendermint/tmlibs"
   version = "~0.8.3-rc0"
+
+[[constraint]]
+  name = "github.com/cosmos/bech32cosmos"
+  branch = "master"
   
 # this got updated and broke, so locked to an old working commit ...
 [[override]]
   name = "google.golang.org/genproto"
   revision = "7fd901a49ba6a7f87732eb344f6e3c5b19d1b200"
 
-  [[constraint]]
-  name = "github.com/cosmos/bech32cosmos"
-  branch = "master"
-  
-
 [prune]
   go-tests = true
   unused-packages = true
-
diff --git a/baseapp/baseapp.go b/baseapp/baseapp.go
index 4ce8a05d9b..cdc5ffcf7a 100644
--- a/baseapp/baseapp.go
+++ b/baseapp/baseapp.go
@@ -65,9 +65,10 @@ type BaseApp struct {
 	// See methods setCheckState and setDeliverState.
 	// .valUpdates accumulate in DeliverTx and are reset in BeginBlock.
 	// QUESTION: should we put valUpdates in the deliverState.ctx?
-	checkState   *state           // for CheckTx
-	deliverState *state           // for DeliverTx
-	valUpdates   []abci.Validator // cached validator changes from DeliverTx
+	checkState       *state           // for CheckTx
+	deliverState     *state           // for DeliverTx
+	valUpdates       []abci.Validator // cached validator changes from DeliverTx
+	absentValidators [][]byte         // absent validators from begin block
 }
 
 var _ abci.Application = (*BaseApp)(nil)
@@ -384,6 +385,8 @@ func (app *BaseApp) BeginBlock(req abci.RequestBeginBlock) (res abci.ResponseBeg
 	if app.beginBlocker != nil {
 		res = app.beginBlocker(app.deliverState.ctx, req)
 	}
+	// set the absent validators for addition to context in deliverTx
+	app.absentValidators = req.AbsentValidators
 	return
 }
 
@@ -493,6 +496,7 @@ func (app *BaseApp) runTx(mode runTxMode, txBytes []byte, tx sdk.Tx) (result sdk
 		ctx = app.checkState.ctx.WithTxBytes(txBytes)
 	} else {
 		ctx = app.deliverState.ctx.WithTxBytes(txBytes)
+		ctx = ctx.WithAbsentValidators(app.absentValidators)
 	}
 
 	// Simulate a DeliverTx for gas calculation
diff --git a/baseapp/baseapp_test.go b/baseapp/baseapp_test.go
index 61498b1b19..0b825e1ee8 100644
--- a/baseapp/baseapp_test.go
+++ b/baseapp/baseapp_test.go
@@ -183,7 +183,7 @@ func TestInitChainer(t *testing.T) {
 
 	// set initChainer and try again - should see the value
 	app.SetInitChainer(initChainer)
-	app.InitChain(abci.RequestInitChain{AppStateBytes: []byte("{}")}) // must have valid JSON genesis file, even if empty
+	app.InitChain(abci.RequestInitChain{GenesisBytes: []byte("{}")}) // must have valid JSON genesis file, even if empty
 	app.Commit()
 	res = app.Query(query)
 	assert.Equal(t, value, res.Value)
diff --git a/cmd/gaia/app/app.go b/cmd/gaia/app/app.go
index dbecada004..4fdb6a6c92 100644
--- a/cmd/gaia/app/app.go
+++ b/cmd/gaia/app/app.go
@@ -15,6 +15,7 @@ import (
 	"github.com/cosmos/cosmos-sdk/x/auth"
 	"github.com/cosmos/cosmos-sdk/x/bank"
 	"github.com/cosmos/cosmos-sdk/x/ibc"
+	"github.com/cosmos/cosmos-sdk/x/slashing"
 	"github.com/cosmos/cosmos-sdk/x/stake"
 )
 
@@ -34,10 +35,11 @@ type GaiaApp struct {
 	cdc *wire.Codec
 
 	// keys to access the substores
-	keyMain    *sdk.KVStoreKey
-	keyAccount *sdk.KVStoreKey
-	keyIBC     *sdk.KVStoreKey
-	keyStake   *sdk.KVStoreKey
+	keyMain     *sdk.KVStoreKey
+	keyAccount  *sdk.KVStoreKey
+	keyIBC      *sdk.KVStoreKey
+	keyStake    *sdk.KVStoreKey
+	keySlashing *sdk.KVStoreKey
 
 	// Manage getting and setting accounts
 	accountMapper       auth.AccountMapper
@@ -45,6 +47,7 @@ type GaiaApp struct {
 	coinKeeper          bank.Keeper
 	ibcMapper           ibc.Mapper
 	stakeKeeper         stake.Keeper
+	slashingKeeper      slashing.Keeper
 }
 
 func NewGaiaApp(logger log.Logger, db dbm.DB) *GaiaApp {
@@ -52,12 +55,13 @@ func NewGaiaApp(logger log.Logger, db dbm.DB) *GaiaApp {
 
 	// create your application object
 	var app = &GaiaApp{
-		BaseApp:    bam.NewBaseApp(appName, cdc, logger, db),
-		cdc:        cdc,
-		keyMain:    sdk.NewKVStoreKey("main"),
-		keyAccount: sdk.NewKVStoreKey("acc"),
-		keyIBC:     sdk.NewKVStoreKey("ibc"),
-		keyStake:   sdk.NewKVStoreKey("stake"),
+		BaseApp:     bam.NewBaseApp(appName, cdc, logger, db),
+		cdc:         cdc,
+		keyMain:     sdk.NewKVStoreKey("main"),
+		keyAccount:  sdk.NewKVStoreKey("acc"),
+		keyIBC:      sdk.NewKVStoreKey("ibc"),
+		keyStake:    sdk.NewKVStoreKey("stake"),
+		keySlashing: sdk.NewKVStoreKey("slashing"),
 	}
 
 	// define the accountMapper
@@ -71,6 +75,7 @@ func NewGaiaApp(logger log.Logger, db dbm.DB) *GaiaApp {
 	app.coinKeeper = bank.NewKeeper(app.accountMapper)
 	app.ibcMapper = ibc.NewMapper(app.cdc, app.keyIBC, app.RegisterCodespace(ibc.DefaultCodespace))
 	app.stakeKeeper = stake.NewKeeper(app.cdc, app.keyStake, app.coinKeeper, app.RegisterCodespace(stake.DefaultCodespace))
+	app.slashingKeeper = slashing.NewKeeper(app.cdc, app.keySlashing, app.stakeKeeper, app.RegisterCodespace(slashing.DefaultCodespace))
 
 	// register message routes
 	app.Router().
@@ -80,9 +85,10 @@ func NewGaiaApp(logger log.Logger, db dbm.DB) *GaiaApp {
 
 	// initialize BaseApp
 	app.SetInitChainer(app.initChainer)
+	app.SetBeginBlocker(slashing.NewBeginBlocker(app.slashingKeeper))
 	app.SetEndBlocker(stake.NewEndBlocker(app.stakeKeeper))
-	app.MountStoresIAVL(app.keyMain, app.keyAccount, app.keyIBC, app.keyStake)
 	app.SetAnteHandler(auth.NewAnteHandler(app.accountMapper, app.feeCollectionKeeper))
+	app.MountStoresIAVL(app.keyMain, app.keyAccount, app.keyIBC, app.keyStake, app.keySlashing)
 	err := app.LoadLatestVersion(app.keyMain)
 	if err != nil {
 		cmn.Exit(err.Error())
@@ -97,6 +103,7 @@ func MakeCodec() *wire.Codec {
 	ibc.RegisterWire(cdc)
 	bank.RegisterWire(cdc)
 	stake.RegisterWire(cdc)
+	slashing.RegisterWire(cdc)
 	auth.RegisterWire(cdc)
 	sdk.RegisterWire(cdc)
 	wire.RegisterCrypto(cdc)
@@ -105,7 +112,8 @@ func MakeCodec() *wire.Codec {
 
 // custom logic for gaia initialization
 func (app *GaiaApp) initChainer(ctx sdk.Context, req abci.RequestInitChain) abci.ResponseInitChain {
-	stateJSON := req.AppStateBytes
+	stateJSON := req.GenesisBytes
+	// TODO is this now the whole genesis file?
 
 	var genesisState GenesisState
 	err := app.cdc.UnmarshalJSON(stateJSON, &genesisState)
diff --git a/examples/basecoin/app/app.go b/examples/basecoin/app/app.go
index 086fa32b36..a0b1f86ad6 100644
--- a/examples/basecoin/app/app.go
+++ b/examples/basecoin/app/app.go
@@ -104,7 +104,7 @@ func MakeCodec() *wire.Codec {
 
 // Custom logic for basecoin initialization
 func (app *BasecoinApp) initChainer(ctx sdk.Context, req abci.RequestInitChain) abci.ResponseInitChain {
-	stateJSON := req.AppStateBytes
+	stateJSON := req.GenesisBytes
 
 	genesisState := new(types.GenesisState)
 	err := app.cdc.UnmarshalJSON(stateJSON, genesisState)
diff --git a/examples/democoin/app/app.go b/examples/democoin/app/app.go
index 2075a64da0..b8b8642cf3 100644
--- a/examples/democoin/app/app.go
+++ b/examples/democoin/app/app.go
@@ -118,7 +118,7 @@ func MakeCodec() *wire.Codec {
 // custom logic for democoin initialization
 func (app *DemocoinApp) initChainerFn(coolKeeper cool.Keeper, powKeeper pow.Keeper) sdk.InitChainer {
 	return func(ctx sdk.Context, req abci.RequestInitChain) abci.ResponseInitChain {
-		stateJSON := req.AppStateBytes
+		stateJSON := req.GenesisBytes
 
 		genesisState := new(types.GenesisState)
 		err := app.cdc.UnmarshalJSON(stateJSON, genesisState)
diff --git a/examples/democoin/x/simplestake/keeper_test.go b/examples/democoin/x/simplestake/keeper_test.go
index 515c19cc59..15bd14c79b 100644
--- a/examples/democoin/x/simplestake/keeper_test.go
+++ b/examples/democoin/x/simplestake/keeper_test.go
@@ -35,9 +35,9 @@ func TestKeeperGetSet(t *testing.T) {
 	cdc := wire.NewCodec()
 	auth.RegisterBaseAccount(cdc)
 
-	ctx := sdk.NewContext(ms, abci.Header{}, false, nil, log.NewNopLogger())
 	accountMapper := auth.NewAccountMapper(cdc, authKey, &auth.BaseAccount{})
 	stakeKeeper := NewKeeper(capKey, bank.NewKeeper(accountMapper), DefaultCodespace)
+	ctx := sdk.NewContext(ms, abci.Header{}, false, nil, log.NewNopLogger())
 	addr := sdk.Address([]byte("some-address"))
 
 	bi := stakeKeeper.getBondInfo(ctx, addr)
diff --git a/mock/app.go b/mock/app.go
index ab1a8447a5..09d7a658c7 100644
--- a/mock/app.go
+++ b/mock/app.go
@@ -88,7 +88,7 @@ type GenesisJSON struct {
 // with key/value pairs
 func InitChainer(key sdk.StoreKey) func(sdk.Context, abci.RequestInitChain) abci.ResponseInitChain {
 	return func(ctx sdk.Context, req abci.RequestInitChain) abci.ResponseInitChain {
-		stateJSON := req.AppStateBytes
+		stateJSON := req.GenesisBytes
 
 		genesisState := new(GenesisJSON)
 		err := json.Unmarshal(stateJSON, genesisState)
diff --git a/mock/app_test.go b/mock/app_test.go
index be1d778295..50b0761c17 100644
--- a/mock/app_test.go
+++ b/mock/app_test.go
@@ -26,7 +26,7 @@ func TestInitApp(t *testing.T) {
 
 	//TODO test validators in the init chain?
 	req := abci.RequestInitChain{
-		AppStateBytes: appState,
+		GenesisBytes: appState,
 	}
 	app.InitChain(req)
 	app.Commit()
diff --git a/types/context.go b/types/context.go
index 4ab0a5d093..10ae99724f 100644
--- a/types/context.go
+++ b/types/context.go
@@ -31,6 +31,7 @@ type Context struct {
 
 // create a new context
 func NewContext(ms MultiStore, header abci.Header, isCheckTx bool, txBytes []byte, logger log.Logger) Context {
+
 	c := Context{
 		Context: context.Background(),
 		pst:     newThePast(),
@@ -43,6 +44,7 @@ func NewContext(ms MultiStore, header abci.Header, isCheckTx bool, txBytes []byt
 	c = c.WithIsCheckTx(isCheckTx)
 	c = c.WithTxBytes(txBytes)
 	c = c.WithLogger(logger)
+	c = c.WithAbsentValidators(nil)
 	c = c.WithGasMeter(NewInfiniteGasMeter())
 	return c
 }
@@ -128,6 +130,7 @@ const (
 	contextKeyIsCheckTx
 	contextKeyTxBytes
 	contextKeyLogger
+	contextKeyAbsentValidators
 	contextKeyGasMeter
 )
 
@@ -157,6 +160,9 @@ func (c Context) TxBytes() []byte {
 func (c Context) Logger() log.Logger {
 	return c.Value(contextKeyLogger).(log.Logger)
 }
+func (c Context) AbsentValidators() [][]byte {
+	return c.Value(contextKeyAbsentValidators).([][]byte)
+}
 func (c Context) GasMeter() GasMeter {
 	return c.Value(contextKeyGasMeter).(GasMeter)
 }
@@ -182,6 +188,9 @@ func (c Context) WithTxBytes(txBytes []byte) Context {
 func (c Context) WithLogger(logger log.Logger) Context {
 	return c.withValue(contextKeyLogger, logger)
 }
+func (c Context) WithAbsentValidators(AbsentValidators [][]byte) Context {
+	return c.withValue(contextKeyAbsentValidators, AbsentValidators)
+}
 func (c Context) WithGasMeter(meter GasMeter) Context {
 	return c.withValue(contextKeyGasMeter, meter)
 }
diff --git a/types/stake.go b/types/stake.go
index 6a1a3a95f6..bfcef7fa0c 100644
--- a/types/stake.go
+++ b/types/stake.go
@@ -56,8 +56,11 @@ type ValidatorSet interface {
 	IterateValidatorsBonded(Context,
 		func(index int64, validator Validator) (stop bool))
 
-	Validator(Context, Address) Validator // get a particular validator by owner address
-	TotalPower(Context) Rat               // total power of the validator set
+	Validator(Context, Address) Validator     // get a particular validator by owner address
+	TotalPower(Context) Rat                   // total power of the validator set
+	Slash(Context, crypto.PubKey, int64, Rat) // slash the validator and delegators of the validator, specifying offence height & slash fraction
+	Revoke(Context, crypto.PubKey)            // revoke a validator
+	Unrevoke(Context, crypto.PubKey)          // unrevoke a validator
 }
 
 //_______________________________________________________________________________
diff --git a/types/tags.go b/types/tags.go
index 95a826fd78..5a8eb1f473 100644
--- a/types/tags.go
+++ b/types/tags.go
@@ -25,6 +25,11 @@ func (t Tags) AppendTags(a Tags) Tags {
 	return append(t, a...)
 }
 
+// Turn tags into KVPair list
+func (t Tags) ToKVPairs() []cmn.KVPair {
+	return []cmn.KVPair(t)
+}
+
 // New variadic tags, must be k string, v []byte repeating
 func NewTags(tags ...interface{}) Tags {
 	var ret Tags
diff --git a/x/slashing/errors.go b/x/slashing/errors.go
new file mode 100644
index 0000000000..087dc03141
--- /dev/null
+++ b/x/slashing/errors.go
@@ -0,0 +1,52 @@
+//nolint
+package slashing
+
+import (
+	sdk "github.com/cosmos/cosmos-sdk/types"
+)
+
+// Local code type
+type CodeType = sdk.CodeType
+
+const (
+	// Default slashing codespace
+	DefaultCodespace sdk.CodespaceType = 10
+
+	// Invalid validator
+	CodeInvalidValidator CodeType = 201
+	// Validator jailed
+	CodeValidatorJailed CodeType = 202
+)
+
+func ErrNoValidatorForAddress(codespace sdk.CodespaceType) sdk.Error {
+	return newError(codespace, CodeInvalidValidator, "That address is not associated with any known validator")
+}
+func ErrBadValidatorAddr(codespace sdk.CodespaceType) sdk.Error {
+	return newError(codespace, CodeInvalidValidator, "Validator does not exist for that address")
+}
+func ErrValidatorJailed(codespace sdk.CodespaceType) sdk.Error {
+	return newError(codespace, CodeValidatorJailed, "Validator jailed, cannot yet be unrevoked")
+}
+
+func codeToDefaultMsg(code CodeType) string {
+	switch code {
+	case CodeInvalidValidator:
+		return "Invalid Validator"
+	case CodeValidatorJailed:
+		return "Validator Jailed"
+	default:
+		return sdk.CodeToDefaultMsg(code)
+	}
+}
+
+func msgOrDefaultMsg(msg string, code CodeType) string {
+	if msg != "" {
+		return msg
+	}
+	return codeToDefaultMsg(code)
+}
+
+func newError(codespace sdk.CodespaceType, code CodeType, msg string) sdk.Error {
+	msg = msgOrDefaultMsg(msg, code)
+	return sdk.NewError(codespace, code, msg)
+}
diff --git a/x/slashing/handler.go b/x/slashing/handler.go
new file mode 100644
index 0000000000..98e9d30ada
--- /dev/null
+++ b/x/slashing/handler.go
@@ -0,0 +1,58 @@
+package slashing
+
+import (
+	sdk "github.com/cosmos/cosmos-sdk/types"
+)
+
+func NewHandler(k Keeper) sdk.Handler {
+	return func(ctx sdk.Context, msg sdk.Msg) sdk.Result {
+		// NOTE msg already has validate basic run
+		switch msg := msg.(type) {
+		case MsgUnrevoke:
+			return handleMsgUnrevoke(ctx, msg, k)
+		default:
+			return sdk.ErrTxDecode("invalid message parse in staking module").Result()
+		}
+	}
+}
+
+// Validators must submit a transaction to unrevoke itself after
+// having been revoked (and thus unbonded) for downtime
+func handleMsgUnrevoke(ctx sdk.Context, msg MsgUnrevoke, k Keeper) sdk.Result {
+
+	// Validator must exist
+	validator := k.stakeKeeper.Validator(ctx, msg.ValidatorAddr)
+	if validator == nil {
+		return ErrNoValidatorForAddress(k.codespace).Result()
+	}
+
+	addr := validator.GetPubKey().Address()
+
+	// Signing info must exist
+	info, found := k.getValidatorSigningInfo(ctx, addr)
+	if !found {
+		return ErrNoValidatorForAddress(k.codespace).Result()
+	}
+
+	// Cannot be unrevoked until out of jail
+	if ctx.BlockHeader().Time < info.JailedUntil {
+		return ErrValidatorJailed(k.codespace).Result()
+	}
+
+	if ctx.IsCheckTx() {
+		return sdk.Result{}
+	}
+
+	// Update the starting height (so the validator can't be immediately revoked again)
+	info.StartHeight = ctx.BlockHeight()
+	k.setValidatorSigningInfo(ctx, addr, info)
+
+	// Unrevoke the validator
+	k.stakeKeeper.Unrevoke(ctx, validator.GetPubKey())
+
+	tags := sdk.NewTags("action", []byte("unrevoke"), "validator", msg.ValidatorAddr.Bytes())
+
+	return sdk.Result{
+		Tags: tags,
+	}
+}
diff --git a/x/slashing/keeper.go b/x/slashing/keeper.go
new file mode 100644
index 0000000000..a37c5a07b8
--- /dev/null
+++ b/x/slashing/keeper.go
@@ -0,0 +1,91 @@
+package slashing
+
+import (
+	"fmt"
+
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	"github.com/cosmos/cosmos-sdk/wire"
+	"github.com/cosmos/cosmos-sdk/x/stake"
+	crypto "github.com/tendermint/go-crypto"
+)
+
+// Keeper of the slashing store
+type Keeper struct {
+	storeKey    sdk.StoreKey
+	cdc         *wire.Codec
+	stakeKeeper stake.Keeper
+
+	// codespace
+	codespace sdk.CodespaceType
+}
+
+// NewKeeper creates a slashing keeper
+func NewKeeper(cdc *wire.Codec, key sdk.StoreKey, sk stake.Keeper, codespace sdk.CodespaceType) Keeper {
+	keeper := Keeper{
+		storeKey:    key,
+		cdc:         cdc,
+		stakeKeeper: sk,
+		codespace:   codespace,
+	}
+	return keeper
+}
+
+// handle a validator signing two blocks at the same height
+func (k Keeper) handleDoubleSign(ctx sdk.Context, height int64, timestamp int64, pubkey crypto.PubKey) {
+	logger := ctx.Logger().With("module", "x/slashing")
+	age := ctx.BlockHeader().Time - timestamp
+
+	// Double sign too old
+	if age > MaxEvidenceAge {
+		logger.Info(fmt.Sprintf("Ignored double sign from %s at height %d, age of %d past max age of %d", pubkey.Address(), height, age, MaxEvidenceAge))
+		return
+	}
+
+	// Double sign confirmed
+	logger.Info(fmt.Sprintf("Confirmed double sign from %s at height %d, age of %d less than max age of %d", pubkey.Address(), height, age, MaxEvidenceAge))
+	k.stakeKeeper.Slash(ctx, pubkey, height, SlashFractionDoubleSign)
+}
+
+// handle a validator signature, must be called once per validator per block
+func (k Keeper) handleValidatorSignature(ctx sdk.Context, pubkey crypto.PubKey, signed bool) {
+	logger := ctx.Logger().With("module", "x/slashing")
+	height := ctx.BlockHeight()
+	if !signed {
+		logger.Info(fmt.Sprintf("Absent validator %s at height %d", pubkey.Address(), height))
+	}
+	address := pubkey.Address()
+
+	// Local index, so counts blocks validator *should* have signed
+	// Will use the 0-value default signing info if not present
+	signInfo, _ := k.getValidatorSigningInfo(ctx, address)
+	index := signInfo.IndexOffset % SignedBlocksWindow
+	signInfo.IndexOffset++
+
+	// Update signed block bit array & counter
+	// This counter just tracks the sum of the bit array
+	// That way we avoid needing to read/write the whole array each time
+	previous := k.getValidatorSigningBitArray(ctx, address, index)
+	if previous == signed {
+		// Array value at this index has not changed, no need to update counter
+	} else if previous && !signed {
+		// Array value has changed from signed to unsigned, decrement counter
+		k.setValidatorSigningBitArray(ctx, address, index, false)
+		signInfo.SignedBlocksCounter--
+	} else if !previous && signed {
+		// Array value has changed from unsigned to signed, increment counter
+		k.setValidatorSigningBitArray(ctx, address, index, true)
+		signInfo.SignedBlocksCounter++
+	}
+
+	minHeight := signInfo.StartHeight + SignedBlocksWindow
+	if height > minHeight && signInfo.SignedBlocksCounter < MinSignedPerWindow {
+		// Downtime confirmed, slash, revoke, and jail the validator
+		logger.Info(fmt.Sprintf("Validator %s past min height of %d and below signed blocks threshold of %d", pubkey.Address(), minHeight, MinSignedPerWindow))
+		k.stakeKeeper.Slash(ctx, pubkey, height, SlashFractionDowntime)
+		k.stakeKeeper.Revoke(ctx, pubkey)
+		signInfo.JailedUntil = ctx.BlockHeader().Time + DowntimeUnbondDuration
+	}
+
+	// Set the updated signing info
+	k.setValidatorSigningInfo(ctx, address, signInfo)
+}
diff --git a/x/slashing/keeper_test.go b/x/slashing/keeper_test.go
new file mode 100644
index 0000000000..3d6da8c232
--- /dev/null
+++ b/x/slashing/keeper_test.go
@@ -0,0 +1,131 @@
+package slashing
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	abci "github.com/tendermint/abci/types"
+
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	"github.com/cosmos/cosmos-sdk/x/stake"
+)
+
+func TestHandleDoubleSign(t *testing.T) {
+
+	// initial setup
+	ctx, ck, sk, keeper := createTestInput(t)
+	addr, val, amt := addrs[0], pks[0], int64(100)
+	got := stake.NewHandler(sk)(ctx, newTestMsgDeclareCandidacy(addr, val, amt))
+	require.True(t, got.IsOK())
+	sk.Tick(ctx)
+	require.Equal(t, ck.GetCoins(ctx, addr), sdk.Coins{{sk.GetParams(ctx).BondDenom, initCoins - amt}})
+	require.Equal(t, sdk.NewRat(amt), sk.Validator(ctx, addr).GetPower())
+
+	// double sign less than max age
+	keeper.handleDoubleSign(ctx, 0, 0, val)
+	require.Equal(t, sdk.NewRat(amt).Mul(sdk.NewRat(19).Quo(sdk.NewRat(20))), sk.Validator(ctx, addr).GetPower())
+	ctx = ctx.WithBlockHeader(abci.Header{Time: 300})
+
+	// double sign past max age
+	keeper.handleDoubleSign(ctx, 0, 0, val)
+	require.Equal(t, sdk.NewRat(amt).Mul(sdk.NewRat(19).Quo(sdk.NewRat(20))), sk.Validator(ctx, addr).GetPower())
+}
+
+func TestHandleAbsentValidator(t *testing.T) {
+
+	// initial setup
+	ctx, ck, sk, keeper := createTestInput(t)
+	addr, val, amt := addrs[0], pks[0], int64(100)
+	sh := stake.NewHandler(sk)
+	slh := NewHandler(keeper)
+	got := sh(ctx, newTestMsgDeclareCandidacy(addr, val, amt))
+	require.True(t, got.IsOK())
+	sk.Tick(ctx)
+	require.Equal(t, ck.GetCoins(ctx, addr), sdk.Coins{{sk.GetParams(ctx).BondDenom, initCoins - amt}})
+	require.Equal(t, sdk.NewRat(amt), sk.Validator(ctx, addr).GetPower())
+	info, found := keeper.getValidatorSigningInfo(ctx, val.Address())
+	require.False(t, found)
+	require.Equal(t, int64(0), info.StartHeight)
+	require.Equal(t, int64(0), info.IndexOffset)
+	require.Equal(t, int64(0), info.SignedBlocksCounter)
+	require.Equal(t, int64(0), info.JailedUntil)
+	height := int64(0)
+
+	// 1000 first blocks OK
+	for ; height < 1000; height++ {
+		ctx = ctx.WithBlockHeight(height)
+		keeper.handleValidatorSignature(ctx, val, true)
+	}
+	info, found = keeper.getValidatorSigningInfo(ctx, val.Address())
+	require.True(t, found)
+	require.Equal(t, int64(0), info.StartHeight)
+	require.Equal(t, SignedBlocksWindow, info.SignedBlocksCounter)
+
+	// 50 blocks missed
+	for ; height < 1050; height++ {
+		ctx = ctx.WithBlockHeight(height)
+		keeper.handleValidatorSignature(ctx, val, false)
+	}
+	info, found = keeper.getValidatorSigningInfo(ctx, val.Address())
+	require.True(t, found)
+	require.Equal(t, int64(0), info.StartHeight)
+	require.Equal(t, SignedBlocksWindow-50, info.SignedBlocksCounter)
+
+	// validator should be bonded still
+	validator, _ := sk.GetValidatorByPubKey(ctx, val)
+	require.Equal(t, sdk.Bonded, validator.GetStatus())
+	pool := sk.GetPool(ctx)
+	require.Equal(t, int64(100), pool.BondedTokens)
+
+	// 51st block missed
+	ctx = ctx.WithBlockHeight(height)
+	keeper.handleValidatorSignature(ctx, val, false)
+	info, found = keeper.getValidatorSigningInfo(ctx, val.Address())
+	require.True(t, found)
+	require.Equal(t, int64(0), info.StartHeight)
+	require.Equal(t, SignedBlocksWindow-51, info.SignedBlocksCounter)
+
+	// validator should have been revoked
+	validator, _ = sk.GetValidatorByPubKey(ctx, val)
+	require.Equal(t, sdk.Unbonded, validator.GetStatus())
+
+	// unrevocation should fail prior to jail expiration
+	got = slh(ctx, NewMsgUnrevoke(addr))
+	require.False(t, got.IsOK())
+
+	// unrevocation should succeed after jail expiration
+	ctx = ctx.WithBlockHeader(abci.Header{Time: int64(86400 * 2)})
+	got = slh(ctx, NewMsgUnrevoke(addr))
+	require.True(t, got.IsOK())
+
+	// validator should be rebonded now
+	validator, _ = sk.GetValidatorByPubKey(ctx, val)
+	require.Equal(t, sdk.Bonded, validator.GetStatus())
+
+	// validator should have been slashed
+	pool = sk.GetPool(ctx)
+	require.Equal(t, int64(99), pool.BondedTokens)
+
+	// validator start height should have been changed
+	info, found = keeper.getValidatorSigningInfo(ctx, val.Address())
+	require.True(t, found)
+	require.Equal(t, height, info.StartHeight)
+	require.Equal(t, SignedBlocksWindow-51, info.SignedBlocksCounter)
+
+	// validator should not be immediately revoked again
+	height++
+	ctx = ctx.WithBlockHeight(height)
+	keeper.handleValidatorSignature(ctx, val, false)
+	validator, _ = sk.GetValidatorByPubKey(ctx, val)
+	require.Equal(t, sdk.Bonded, validator.GetStatus())
+
+	// validator should be revoked again after 100 unsigned blocks
+	nextHeight := height + 100
+	for ; height <= nextHeight; height++ {
+		ctx = ctx.WithBlockHeight(height)
+		keeper.handleValidatorSignature(ctx, val, false)
+	}
+	validator, _ = sk.GetValidatorByPubKey(ctx, val)
+	require.Equal(t, sdk.Unbonded, validator.GetStatus())
+}
diff --git a/x/slashing/msg.go b/x/slashing/msg.go
new file mode 100644
index 0000000000..d2676af81a
--- /dev/null
+++ b/x/slashing/msg.go
@@ -0,0 +1,46 @@
+package slashing
+
+import (
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	"github.com/cosmos/cosmos-sdk/wire"
+)
+
+var cdc = wire.NewCodec()
+
+// name to identify transaction types
+const MsgType = "slashing"
+
+// verify interface at compile time
+var _ sdk.Msg = &MsgUnrevoke{}
+
+// MsgUnrevoke - struct for unrevoking revoked validator
+type MsgUnrevoke struct {
+	ValidatorAddr sdk.Address `json:"address"` // address of the validator owner
+}
+
+func NewMsgUnrevoke(validatorAddr sdk.Address) MsgUnrevoke {
+	return MsgUnrevoke{
+		ValidatorAddr: validatorAddr,
+	}
+}
+
+//nolint
+func (msg MsgUnrevoke) Type() string              { return MsgType }
+func (msg MsgUnrevoke) GetSigners() []sdk.Address { return []sdk.Address{msg.ValidatorAddr} }
+
+// get the bytes for the message signer to sign on
+func (msg MsgUnrevoke) GetSignBytes() []byte {
+	b, err := cdc.MarshalJSON(msg)
+	if err != nil {
+		panic(err)
+	}
+	return b
+}
+
+// quick validity check
+func (msg MsgUnrevoke) ValidateBasic() sdk.Error {
+	if msg.ValidatorAddr == nil {
+		return ErrBadValidatorAddr(DefaultCodespace)
+	}
+	return nil
+}
diff --git a/x/slashing/params.go b/x/slashing/params.go
new file mode 100644
index 0000000000..3bba85fa66
--- /dev/null
+++ b/x/slashing/params.go
@@ -0,0 +1,37 @@
+package slashing
+
+import (
+	sdk "github.com/cosmos/cosmos-sdk/types"
+)
+
+const (
+	// MaxEvidenceAge - Max age for evidence - 21 days (3 weeks)
+	// TODO Should this be a governance parameter or just modifiable with SoftwareUpgradeProposals?
+	// MaxEvidenceAge = 60 * 60 * 24 * 7 * 3
+	// TODO Temporarily set to 2 minutes for testnets.
+	MaxEvidenceAge int64 = 60 * 2
+
+	// SignedBlocksWindow - sliding window for downtime slashing
+	// TODO Governance parameter?
+	// TODO Temporarily set to 100 blocks for testnets
+	SignedBlocksWindow int64 = 100
+
+	// Downtime slashing threshold - 50%
+	// TODO Governance parameter?
+	MinSignedPerWindow int64 = SignedBlocksWindow / 2
+
+	// Downtime unbond duration
+	// TODO Governance parameter?
+	// TODO Temporarily set to 10 minutes for testnets
+	DowntimeUnbondDuration int64 = 60 * 10
+)
+
+var (
+	// SlashFractionDoubleSign - currently 5%
+	// TODO Governance parameter?
+	SlashFractionDoubleSign = sdk.NewRat(1).Quo(sdk.NewRat(20))
+
+	// SlashFractionDowntime - currently 1%
+	// TODO Governance parameter?
+	SlashFractionDowntime = sdk.NewRat(1).Quo(sdk.NewRat(100))
+)
diff --git a/x/slashing/signing_info.go b/x/slashing/signing_info.go
new file mode 100644
index 0000000000..05285b6809
--- /dev/null
+++ b/x/slashing/signing_info.go
@@ -0,0 +1,66 @@
+package slashing
+
+import (
+	"encoding/binary"
+
+	sdk "github.com/cosmos/cosmos-sdk/types"
+)
+
+// Stored by *validator* address (not owner address)
+func (k Keeper) getValidatorSigningInfo(ctx sdk.Context, address sdk.Address) (info validatorSigningInfo, found bool) {
+	store := ctx.KVStore(k.storeKey)
+	bz := store.Get(validatorSigningInfoKey(address))
+	if bz == nil {
+		found = false
+		return
+	}
+	k.cdc.MustUnmarshalBinary(bz, &info)
+	found = true
+	return
+}
+
+// Stored by *validator* address (not owner address)
+func (k Keeper) setValidatorSigningInfo(ctx sdk.Context, address sdk.Address, info validatorSigningInfo) {
+	store := ctx.KVStore(k.storeKey)
+	bz := k.cdc.MustMarshalBinary(info)
+	store.Set(validatorSigningInfoKey(address), bz)
+}
+
+// Stored by *validator* address (not owner address)
+func (k Keeper) getValidatorSigningBitArray(ctx sdk.Context, address sdk.Address, index int64) (signed bool) {
+	store := ctx.KVStore(k.storeKey)
+	bz := store.Get(validatorSigningBitArrayKey(address, index))
+	if bz == nil {
+		// lazy: treat empty key as unsigned
+		signed = false
+		return
+	}
+	k.cdc.MustUnmarshalBinary(bz, &signed)
+	return
+}
+
+// Stored by *validator* address (not owner address)
+func (k Keeper) setValidatorSigningBitArray(ctx sdk.Context, address sdk.Address, index int64, signed bool) {
+	store := ctx.KVStore(k.storeKey)
+	bz := k.cdc.MustMarshalBinary(signed)
+	store.Set(validatorSigningBitArrayKey(address, index), bz)
+}
+
+type validatorSigningInfo struct {
+	StartHeight         int64 `json:"start_height"`          // height at which validator was first a candidate OR was unrevoked
+	IndexOffset         int64 `json:"index_offset"`          // index offset into signed block bit array
+	JailedUntil         int64 `json:"jailed_until"`          // timestamp validator cannot be unrevoked until
+	SignedBlocksCounter int64 `json:"signed_blocks_counter"` // signed blocks counter (to avoid scanning the array every time)
+}
+
+// Stored by *validator* address (not owner address)
+func validatorSigningInfoKey(v sdk.Address) []byte {
+	return append([]byte{0x01}, v.Bytes()...)
+}
+
+// Stored by *validator* address (not owner address)
+func validatorSigningBitArrayKey(v sdk.Address, i int64) []byte {
+	b := make([]byte, 8)
+	binary.LittleEndian.PutUint64(b, uint64(i))
+	return append([]byte{0x02}, append(v.Bytes(), b...)...)
+}
diff --git a/x/slashing/signing_info_test.go b/x/slashing/signing_info_test.go
new file mode 100644
index 0000000000..8000d67450
--- /dev/null
+++ b/x/slashing/signing_info_test.go
@@ -0,0 +1,35 @@
+package slashing
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestGetSetValidatorSigningInfo(t *testing.T) {
+	ctx, _, _, keeper := createTestInput(t)
+	info, found := keeper.getValidatorSigningInfo(ctx, addrs[0])
+	require.False(t, found)
+	newInfo := validatorSigningInfo{
+		StartHeight:         int64(4),
+		IndexOffset:         int64(3),
+		JailedUntil:         int64(2),
+		SignedBlocksCounter: int64(10),
+	}
+	keeper.setValidatorSigningInfo(ctx, addrs[0], newInfo)
+	info, found = keeper.getValidatorSigningInfo(ctx, addrs[0])
+	require.True(t, found)
+	require.Equal(t, info.StartHeight, int64(4))
+	require.Equal(t, info.IndexOffset, int64(3))
+	require.Equal(t, info.JailedUntil, int64(2))
+	require.Equal(t, info.SignedBlocksCounter, int64(10))
+}
+
+func TestGetSetValidatorSigningBitArray(t *testing.T) {
+	ctx, _, _, keeper := createTestInput(t)
+	signed := keeper.getValidatorSigningBitArray(ctx, addrs[0], 0)
+	require.False(t, signed) // treat empty key as unsigned
+	keeper.setValidatorSigningBitArray(ctx, addrs[0], 0, true)
+	signed = keeper.getValidatorSigningBitArray(ctx, addrs[0], 0)
+	require.True(t, signed) // now should be signed
+}
diff --git a/x/slashing/test_common.go b/x/slashing/test_common.go
new file mode 100644
index 0000000000..0228e9498b
--- /dev/null
+++ b/x/slashing/test_common.go
@@ -0,0 +1,95 @@
+package slashing
+
+import (
+	"encoding/hex"
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	abci "github.com/tendermint/abci/types"
+	crypto "github.com/tendermint/go-crypto"
+	dbm "github.com/tendermint/tmlibs/db"
+	"github.com/tendermint/tmlibs/log"
+
+	"github.com/cosmos/cosmos-sdk/store"
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	"github.com/cosmos/cosmos-sdk/wire"
+	"github.com/cosmos/cosmos-sdk/x/auth"
+	"github.com/cosmos/cosmos-sdk/x/bank"
+	"github.com/cosmos/cosmos-sdk/x/stake"
+)
+
+var (
+	addrs = []sdk.Address{
+		testAddr("A58856F0FD53BF058B4909A21AEC019107BA6160"),
+		testAddr("A58856F0FD53BF058B4909A21AEC019107BA6161"),
+	}
+	pks = []crypto.PubKey{
+		newPubKey("0B485CFC0EECC619440448436F8FC9DF40566F2369E72400281454CB552AFB50"),
+		newPubKey("0B485CFC0EECC619440448436F8FC9DF40566F2369E72400281454CB552AFB51"),
+	}
+	initCoins int64 = 200
+)
+
+func createTestCodec() *wire.Codec {
+	cdc := wire.NewCodec()
+	sdk.RegisterWire(cdc)
+	auth.RegisterWire(cdc)
+	bank.RegisterWire(cdc)
+	stake.RegisterWire(cdc)
+	wire.RegisterCrypto(cdc)
+	return cdc
+}
+
+func createTestInput(t *testing.T) (sdk.Context, bank.Keeper, stake.Keeper, Keeper) {
+	keyAcc := sdk.NewKVStoreKey("acc")
+	keyStake := sdk.NewKVStoreKey("stake")
+	keySlashing := sdk.NewKVStoreKey("slashing")
+	db := dbm.NewMemDB()
+	ms := store.NewCommitMultiStore(db)
+	ms.MountStoreWithDB(keyAcc, sdk.StoreTypeIAVL, db)
+	ms.MountStoreWithDB(keyStake, sdk.StoreTypeIAVL, db)
+	ms.MountStoreWithDB(keySlashing, sdk.StoreTypeIAVL, db)
+	err := ms.LoadLatestVersion()
+	require.Nil(t, err)
+	ctx := sdk.NewContext(ms, abci.Header{}, false, nil, log.NewTMLogger(os.Stdout))
+	cdc := createTestCodec()
+	accountMapper := auth.NewAccountMapper(cdc, keyAcc, &auth.BaseAccount{})
+	ck := bank.NewKeeper(accountMapper)
+	sk := stake.NewKeeper(cdc, keyStake, ck, stake.DefaultCodespace)
+	genesis := stake.DefaultGenesisState()
+	genesis.Pool.LooseUnbondedTokens = initCoins * int64(len(addrs))
+	stake.InitGenesis(ctx, sk, genesis)
+	for _, addr := range addrs {
+		ck.AddCoins(ctx, addr, sdk.Coins{
+			{sk.GetParams(ctx).BondDenom, initCoins},
+		})
+	}
+	keeper := NewKeeper(cdc, keySlashing, sk, DefaultCodespace)
+	return ctx, ck, sk, keeper
+}
+
+func newPubKey(pk string) (res crypto.PubKey) {
+	pkBytes, err := hex.DecodeString(pk)
+	if err != nil {
+		panic(err)
+	}
+	var pkEd crypto.PubKeyEd25519
+	copy(pkEd[:], pkBytes[:])
+	return pkEd
+}
+
+func testAddr(addr string) sdk.Address {
+	res := []byte(addr)
+	return res
+}
+
+func newTestMsgDeclareCandidacy(address sdk.Address, pubKey crypto.PubKey, amt int64) stake.MsgDeclareCandidacy {
+	return stake.MsgDeclareCandidacy{
+		Description:   stake.Description{},
+		ValidatorAddr: address,
+		PubKey:        pubKey,
+		Bond:          sdk.Coin{"steak", amt},
+	}
+}
diff --git a/x/slashing/tick.go b/x/slashing/tick.go
new file mode 100644
index 0000000000..402c8997b8
--- /dev/null
+++ b/x/slashing/tick.go
@@ -0,0 +1,58 @@
+package slashing
+
+import (
+	"encoding/binary"
+	"fmt"
+
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	abci "github.com/tendermint/abci/types"
+	crypto "github.com/tendermint/go-crypto"
+	tmtypes "github.com/tendermint/tendermint/types"
+)
+
+func NewBeginBlocker(sk Keeper) sdk.BeginBlocker {
+	return func(ctx sdk.Context, req abci.RequestBeginBlock) abci.ResponseBeginBlock {
+		// Tag the height
+		heightBytes := make([]byte, 8)
+		binary.LittleEndian.PutUint64(heightBytes, uint64(req.Header.Height))
+		tags := sdk.NewTags("height", heightBytes)
+
+		// Deal with any equivocation evidence
+		for _, evidence := range req.ByzantineValidators {
+			var pk crypto.PubKey
+			sk.cdc.MustUnmarshalBinary(evidence.PubKey, &pk)
+			switch string(evidence.Type) {
+			case tmtypes.DUPLICATE_VOTE:
+				sk.handleDoubleSign(ctx, evidence.Height, evidence.Time, pk)
+			default:
+				ctx.Logger().With("module", "x/slashing").Error(fmt.Sprintf("Ignored unknown evidence type: %s", string(evidence.Type)))
+			}
+		}
+
+		// Figure out which validators were absent
+		absent := make(map[crypto.PubKey]struct{})
+		for _, pubkey := range req.AbsentValidators {
+			var pk crypto.PubKey
+			sk.cdc.MustUnmarshalBinary(pubkey, &pk)
+			absent[pk] = struct{}{}
+		}
+
+		// Iterate over all the validators which *should* have signed this block
+		sk.stakeKeeper.IterateValidatorsBonded(ctx, func(_ int64, validator sdk.Validator) (stop bool) {
+			pubkey := validator.GetPubKey()
+			present := true
+			if _, ok := absent[pubkey]; ok {
+				present = false
+			}
+			sk.handleValidatorSignature(ctx, pubkey, present)
+			return false
+		})
+
+		// Return the begin block response
+		// TODO Return something composable, so other modules can also have BeginBlockers
+		// TODO Add some more tags so clients can track slashing events
+		return abci.ResponseBeginBlock{
+			Tags: tags.ToKVPairs(),
+		}
+	}
+}
diff --git a/x/slashing/wire.go b/x/slashing/wire.go
new file mode 100644
index 0000000000..465a06587e
--- /dev/null
+++ b/x/slashing/wire.go
@@ -0,0 +1,12 @@
+package slashing
+
+import (
+	"github.com/cosmos/cosmos-sdk/wire"
+)
+
+// Register concrete types on wire codec
+func RegisterWire(cdc *wire.Codec) {
+	cdc.RegisterConcrete(MsgUnrevoke{}, "cosmos-sdk/MsgUnrevoke", nil)
+}
+
+var cdcEmpty = wire.NewCodec()
diff --git a/x/stake/errors.go b/x/stake/errors.go
index 83c38d528d..77090d9dc3 100644
--- a/x/stake/errors.go
+++ b/x/stake/errors.go
@@ -16,6 +16,7 @@ const (
 	CodeInvalidValidator CodeType = 201
 	CodeInvalidBond      CodeType = 202
 	CodeInvalidInput     CodeType = 203
+	CodeValidatorJailed  CodeType = 204
 	CodeUnauthorized     CodeType = sdk.CodeUnauthorized
 	CodeInternal         CodeType = sdk.CodeInternal
 	CodeUnknownRequest   CodeType = sdk.CodeUnknownRequest
diff --git a/x/stake/genesis.go b/x/stake/genesis.go
index be8d0dbe44..0a7c528bf6 100644
--- a/x/stake/genesis.go
+++ b/x/stake/genesis.go
@@ -29,14 +29,25 @@ func DefaultGenesisState() GenesisState {
 
 // InitGenesis - store genesis parameters
 func InitGenesis(ctx sdk.Context, k Keeper, data GenesisState) {
+	store := ctx.KVStore(k.storeKey)
 	k.setPool(ctx, data.Pool)
 	k.setNewParams(ctx, data.Params)
 	for _, validator := range data.Validators {
-		k.updateValidator(ctx, validator)
+
+		// set validator
+		k.setValidator(ctx, validator)
+
+		// manually set indexes for the first time
+		k.setValidatorByPubKeyIndex(ctx, validator)
+		k.setValidatorByPowerIndex(ctx, validator, data.Pool)
+		if validator.Status() == sdk.Bonded {
+			store.Set(GetValidatorsBondedKey(validator.PubKey), validator.Owner)
+		}
 	}
 	for _, bond := range data.Bonds {
 		k.setDelegation(ctx, bond)
 	}
+	k.updateBondedValidatorsFull(ctx, store)
 }
 
 // WriteGenesis - output genesis parameters
diff --git a/x/stake/handler.go b/x/stake/handler.go
index 53653557cc..6f2360adf7 100644
--- a/x/stake/handler.go
+++ b/x/stake/handler.go
@@ -55,6 +55,7 @@ func handleMsgDeclareCandidacy(ctx sdk.Context, msg MsgDeclareCandidacy, k Keepe
 
 	validator := NewValidator(msg.ValidatorAddr, msg.PubKey, msg.Description)
 	k.setValidator(ctx, validator)
+	k.setValidatorByPubKeyIndex(ctx, validator)
 	tags := sdk.NewTags(
 		"action", []byte("declareCandidacy"),
 		"validator", msg.ValidatorAddr.Bytes(),
diff --git a/x/stake/keeper.go b/x/stake/keeper.go
index ce84b1e177..9fd902053a 100644
--- a/x/stake/keeper.go
+++ b/x/stake/keeper.go
@@ -8,6 +8,7 @@ import (
 	"github.com/cosmos/cosmos-sdk/wire"
 	"github.com/cosmos/cosmos-sdk/x/bank"
 	abci "github.com/tendermint/abci/types"
+	crypto "github.com/tendermint/go-crypto"
 )
 
 // keeper of the staking store
@@ -38,6 +39,16 @@ func (k Keeper) GetValidator(ctx sdk.Context, addr sdk.Address) (validator Valid
 	return k.getValidator(store, addr)
 }
 
+// get a single validator by pubkey
+func (k Keeper) GetValidatorByPubKey(ctx sdk.Context, pubkey crypto.PubKey) (validator Validator, found bool) {
+	store := ctx.KVStore(k.storeKey)
+	addr := store.Get(GetValidatorByPubKeyIndexKey(pubkey))
+	if addr == nil {
+		return validator, false
+	}
+	return k.getValidator(store, addr)
+}
+
 // get a single validator (reuse store)
 func (k Keeper) getValidator(store sdk.KVStore, addr sdk.Address) (validator Validator, found bool) {
 	b := store.Get(GetValidatorKey(addr))
@@ -51,10 +62,22 @@ func (k Keeper) getValidator(store sdk.KVStore, addr sdk.Address) (validator Val
 // set the main record holding validator details
 func (k Keeper) setValidator(ctx sdk.Context, validator Validator) {
 	store := ctx.KVStore(k.storeKey)
+	// set main store
 	bz := k.cdc.MustMarshalBinary(validator)
 	store.Set(GetValidatorKey(validator.Owner), bz)
 }
 
+func (k Keeper) setValidatorByPubKeyIndex(ctx sdk.Context, validator Validator) {
+	store := ctx.KVStore(k.storeKey)
+	// set pointer by pubkey
+	store.Set(GetValidatorByPubKeyIndexKey(validator.PubKey), validator.Owner)
+}
+
+func (k Keeper) setValidatorByPowerIndex(ctx sdk.Context, validator Validator, pool Pool) {
+	store := ctx.KVStore(k.storeKey)
+	store.Set(GetValidatorsByPowerKey(validator, pool), validator.Owner)
+}
+
 // Get the set of all validators with no limits, used during genesis dump
 func (k Keeper) getAllValidators(ctx sdk.Context) (validators Validators) {
 	store := ctx.KVStore(k.storeKey)
@@ -203,8 +226,12 @@ func (k Keeper) updateValidator(ctx sdk.Context, validator Validator) Validator
 	oldValidator, oldFound := k.GetValidator(ctx, ownerAddr)
 
 	if validator.Revoked && oldValidator.Status() == sdk.Bonded {
-		validator, pool = validator.UpdateStatus(pool, sdk.Unbonded)
-		k.setPool(ctx, pool)
+		validator = k.unbondValidator(ctx, store, validator)
+
+		// need to also clear the cliff validator spot because the revoke has
+		// opened up a new spot which will be filled when
+		// updateValidatorsBonded is called
+		k.clearCliffValidator(ctx)
 	}
 
 	powerIncreasing := false
@@ -409,7 +436,7 @@ func (k Keeper) updateBondedValidatorsFull(ctx sdk.Context, store sdk.KVStore) {
 }
 
 // perform all the store operations for when a validator status becomes unbonded
-func (k Keeper) unbondValidator(ctx sdk.Context, store sdk.KVStore, validator Validator) {
+func (k Keeper) unbondValidator(ctx sdk.Context, store sdk.KVStore, validator Validator) Validator {
 	pool := k.GetPool(ctx)
 
 	// sanity check
@@ -431,6 +458,7 @@ func (k Keeper) unbondValidator(ctx sdk.Context, store sdk.KVStore, validator Va
 
 	// also remove from the Bonded Validators Store
 	store.Delete(GetValidatorsBondedKey(validator.PubKey))
+	return validator
 }
 
 // perform all the store operations for when a validator status becomes bonded
@@ -470,6 +498,7 @@ func (k Keeper) removeValidator(ctx sdk.Context, address sdk.Address) {
 	store := ctx.KVStore(k.storeKey)
 	pool := k.getPool(store)
 	store.Delete(GetValidatorKey(address))
+	store.Delete(GetValidatorByPubKeyIndexKey(validator.PubKey))
 	store.Delete(GetValidatorsByPowerKey(validator, pool))
 
 	// delete from the current and power weighted validator groups if the validator
@@ -656,6 +685,13 @@ func (k Keeper) setCliffValidator(ctx sdk.Context, validator Validator, pool Poo
 	store.Set(ValidatorCliffKey, validator.Owner)
 }
 
+// clear the current validator and power of the validator on the cliff
+func (k Keeper) clearCliffValidator(ctx sdk.Context) {
+	store := ctx.KVStore(k.storeKey)
+	store.Delete(ValidatorPowerCliffKey)
+	store.Delete(ValidatorCliffKey)
+}
+
 //__________________________________________________________________________
 
 // Implements ValidatorSet
@@ -749,3 +785,46 @@ func (k Keeper) IterateDelegators(ctx sdk.Context, delAddr sdk.Address, fn func(
 	}
 	iterator.Close()
 }
+
+// slash a validator
+func (k Keeper) Slash(ctx sdk.Context, pubkey crypto.PubKey, height int64, fraction sdk.Rat) {
+	// TODO height ignored for now, see https://github.com/cosmos/cosmos-sdk/pull/1011#issuecomment-390253957
+	logger := ctx.Logger().With("module", "x/stake")
+	val, found := k.GetValidatorByPubKey(ctx, pubkey)
+	if !found {
+		panic(fmt.Errorf("Attempted to slash a nonexistent validator with address %s", pubkey.Address()))
+	}
+	sharesToRemove := val.PoolShares.Amount.Mul(fraction)
+	pool := k.GetPool(ctx)
+	val, pool, burned := val.removePoolShares(pool, sharesToRemove)
+	k.setPool(ctx, pool)        // update the pool
+	k.updateValidator(ctx, val) // update the validator, possibly kicking it out
+	logger.Info(fmt.Sprintf("Validator %s slashed by fraction %v, removed %v shares and burned %d tokens", pubkey.Address(), fraction, sharesToRemove, burned))
+	return
+}
+
+// revoke a validator
+func (k Keeper) Revoke(ctx sdk.Context, pubkey crypto.PubKey) {
+	logger := ctx.Logger().With("module", "x/stake")
+	val, found := k.GetValidatorByPubKey(ctx, pubkey)
+	if !found {
+		panic(fmt.Errorf("Validator with pubkey %s not found, cannot revoke", pubkey))
+	}
+	val.Revoked = true
+	k.updateValidator(ctx, val) // update the validator, now revoked
+	logger.Info(fmt.Sprintf("Validator %s revoked", pubkey.Address()))
+	return
+}
+
+// unrevoke a validator
+func (k Keeper) Unrevoke(ctx sdk.Context, pubkey crypto.PubKey) {
+	logger := ctx.Logger().With("module", "x/stake")
+	val, found := k.GetValidatorByPubKey(ctx, pubkey)
+	if !found {
+		panic(fmt.Errorf("Validator with pubkey %s not found, cannot unrevoke", pubkey))
+	}
+	val.Revoked = false
+	k.updateValidator(ctx, val) // update the validator, now unrevoked
+	logger.Info(fmt.Sprintf("Validator %s unrevoked", pubkey.Address()))
+	return
+}
diff --git a/x/stake/keeper_keys.go b/x/stake/keeper_keys.go
index 5a84d08f29..632a86ec3c 100644
--- a/x/stake/keeper_keys.go
+++ b/x/stake/keeper_keys.go
@@ -13,16 +13,17 @@ import (
 //nolint
 var (
 	// Keys for store prefixes
-	ParamKey               = []byte{0x00} // key for parameters relating to staking
-	PoolKey                = []byte{0x01} // key for the staking pools
-	ValidatorsKey          = []byte{0x02} // prefix for each key to a validator
-	ValidatorsBondedKey    = []byte{0x03} // prefix for each key to bonded/actively validating validators
-	ValidatorsByPowerKey   = []byte{0x04} // prefix for each key to a validator sorted by power
-	ValidatorCliffKey      = []byte{0x05} // key for block-local tx index
-	ValidatorPowerCliffKey = []byte{0x06} // key for block-local tx index
-	TendermintUpdatesKey   = []byte{0x07} // prefix for each key to a validator which is being updated
-	DelegationKey          = []byte{0x08} // prefix for each key to a delegator's bond
-	IntraTxCounterKey      = []byte{0x09} // key for block-local tx index
+	ParamKey                   = []byte{0x00} // key for parameters relating to staking
+	PoolKey                    = []byte{0x01} // key for the staking pools
+	ValidatorsKey              = []byte{0x02} // prefix for each key to a validator
+	ValidatorsByPubKeyIndexKey = []byte{0x03} // prefix for each key to a validator by pubkey
+	ValidatorsBondedKey        = []byte{0x04} // prefix for each key to bonded/actively validating validators
+	ValidatorsByPowerKey       = []byte{0x05} // prefix for each key to a validator sorted by power
+	ValidatorCliffKey          = []byte{0x06} // key for block-local tx index
+	ValidatorPowerCliffKey     = []byte{0x07} // key for block-local tx index
+	TendermintUpdatesKey       = []byte{0x08} // prefix for each key to a validator which is being updated
+	DelegationKey              = []byte{0x09} // prefix for each key to a delegator's bond
+	IntraTxCounterKey          = []byte{0x10} // key for block-local tx index
 )
 
 const maxDigitsForAccount = 12 // ~220,000,000 atoms created at launch
@@ -32,6 +33,11 @@ func GetValidatorKey(ownerAddr sdk.Address) []byte {
 	return append(ValidatorsKey, ownerAddr.Bytes()...)
 }
 
+// get the key for the validator with pubkey
+func GetValidatorByPubKeyIndexKey(pubkey crypto.PubKey) []byte {
+	return append(ValidatorsByPubKeyIndexKey, pubkey.Bytes()...)
+}
+
 // get the key for the current validator group, ordered like tendermint
 func GetValidatorsBondedKey(pk crypto.PubKey) []byte {
 	addr := pk.Address()
diff --git a/x/stake/validator.go b/x/stake/validator.go
index cf4ee85fda..729a605a96 100644
--- a/x/stake/validator.go
+++ b/x/stake/validator.go
@@ -47,6 +47,7 @@ func NewValidator(owner sdk.Address, pubKey crypto.PubKey, description Descripti
 	return Validator{
 		Owner:                 owner,
 		PubKey:                pubKey,
+		Revoked:               false,
 		PoolShares:            NewUnbondedShares(sdk.ZeroRat()),
 		DelegatorShares:       sdk.ZeroRat(),
 		Description:           description,
@@ -154,6 +155,23 @@ func (v Validator) UpdateStatus(pool Pool, NewStatus sdk.BondStatus) (Validator,
 	return v, pool
 }
 
+// Remove pool shares
+// Returns corresponding tokens, which could be burned (e.g. when slashing
+// a validator) or redistributed elsewhere
+func (v Validator) removePoolShares(pool Pool, poolShares sdk.Rat) (Validator, Pool, int64) {
+	var tokens int64
+	switch v.Status() {
+	case sdk.Unbonded:
+		pool, tokens = pool.removeSharesUnbonded(poolShares)
+	case sdk.Unbonding:
+		pool, tokens = pool.removeSharesUnbonding(poolShares)
+	case sdk.Bonded:
+		pool, tokens = pool.removeSharesBonded(poolShares)
+	}
+	v.PoolShares.Amount = v.PoolShares.Amount.Sub(poolShares)
+	return v, pool, tokens
+}
+
 // XXX TEST
 // get the power or potential power for a validator
 // if bonded, the power is the BondedShares