diff --git a/client/client.go b/client/client.go
index 092c479a..ddb589a4 100644
--- a/client/client.go
+++ b/client/client.go
@@ -8,10 +8,11 @@ import (
 	cmn "github.com/tendermint/tmlibs/common"
 )
 
-// Client defines an interface for an ABCI client. Client-related errors (e.g.
-// network errors) are returned as a second return value for most calls
-// (sometimes there is no response). Application-related errors are reflected
-// in response via ABCI error codes and logs.
+// Client defines an interface for an ABCI client.
+// All `Async` methods return a `ReqRes` object.
+// All `Sync` methods return the appropriate protobuf ResponseXxx struct and an error.
+// Note these are client errors, eg. ABCI socket connectivity issues.
+// Application-related errors are reflected in response via ABCI error codes and logs.
 type Client interface {
 	cmn.Service
 
@@ -21,28 +22,26 @@ type Client interface {
 	FlushAsync() *ReqRes
 	EchoAsync(msg string) *ReqRes
 	InfoAsync(types.RequestInfo) *ReqRes
-	SetOptionAsync(key string, value string) *ReqRes
+	SetOptionAsync(types.RequestSetOption) *ReqRes
 	DeliverTxAsync(tx []byte) *ReqRes
 	CheckTxAsync(tx []byte) *ReqRes
 	QueryAsync(types.RequestQuery) *ReqRes
 	CommitAsync() *ReqRes
+	InitChainAsync(types.RequestInitChain) *ReqRes
+	BeginBlockAsync(types.RequestBeginBlock) *ReqRes
+	EndBlockAsync(types.RequestEndBlock) *ReqRes
 
 	FlushSync() error
 	EchoSync(msg string) (*types.ResponseEcho, error)
 	InfoSync(types.RequestInfo) (*types.ResponseInfo, error)
-	SetOptionSync(key string, value string) (log string, err error)
+	SetOptionSync(types.RequestSetOption) (*types.ResponseSetOption, error)
 	DeliverTxSync(tx []byte) (*types.ResponseDeliverTx, error)
 	CheckTxSync(tx []byte) (*types.ResponseCheckTx, error)
 	QuerySync(types.RequestQuery) (*types.ResponseQuery, error)
 	CommitSync() (*types.ResponseCommit, error)
-
-	InitChainAsync(types.RequestInitChain) *ReqRes
-	BeginBlockAsync(types.RequestBeginBlock) *ReqRes
-	EndBlockAsync(height uint64) *ReqRes
-
-	InitChainSync(types.RequestInitChain) error
-	BeginBlockSync(types.RequestBeginBlock) error
-	EndBlockSync(height uint64) (*types.ResponseEndBlock, error)
+	InitChainSync(types.RequestInitChain) (*types.ResponseInitChain, error)
+	BeginBlockSync(types.RequestBeginBlock) (*types.ResponseBeginBlock, error)
+	EndBlockSync(types.RequestEndBlock) (*types.ResponseEndBlock, error)
 }
 
 //----------------------------------------
diff --git a/client/grpc_client.go b/client/grpc_client.go
index f7889d69..6079c90c 100644
--- a/client/grpc_client.go
+++ b/client/grpc_client.go
@@ -150,8 +150,8 @@ func (cli *grpcClient) InfoAsync(params types.RequestInfo) *ReqRes {
 	return cli.finishAsyncCall(req, &types.Response{&types.Response_Info{res}})
 }
 
-func (cli *grpcClient) SetOptionAsync(key string, value string) *ReqRes {
-	req := types.ToRequestSetOption(key, value)
+func (cli *grpcClient) SetOptionAsync(params types.RequestSetOption) *ReqRes {
+	req := types.ToRequestSetOption(params)
 	res, err := cli.client.SetOption(context.Background(), req.GetSetOption(), grpc.FailFast(true))
 	if err != nil {
 		cli.StopForError(err)
@@ -213,8 +213,8 @@ func (cli *grpcClient) BeginBlockAsync(params types.RequestBeginBlock) *ReqRes {
 	return cli.finishAsyncCall(req, &types.Response{&types.Response_BeginBlock{res}})
 }
 
-func (cli *grpcClient) EndBlockAsync(height uint64) *ReqRes {
-	req := types.ToRequestEndBlock(height)
+func (cli *grpcClient) EndBlockAsync(params types.RequestEndBlock) *ReqRes {
+	req := types.ToRequestEndBlock(params)
 	res, err := cli.client.EndBlock(context.Background(), req.GetEndBlock(), grpc.FailFast(true))
 	if err != nil {
 		cli.StopForError(err)
@@ -260,12 +260,9 @@ func (cli *grpcClient) InfoSync(req types.RequestInfo) (*types.ResponseInfo, err
 	return reqres.Response.GetInfo(), cli.Error()
 }
 
-func (cli *grpcClient) SetOptionSync(key string, value string) (log string, err error) {
-	reqres := cli.SetOptionAsync(key, value)
-	if err := cli.Error(); err != nil {
-		return "", err
-	}
-	return reqres.Response.GetSetOption().Log, nil
+func (cli *grpcClient) SetOptionSync(req types.RequestSetOption) (*types.ResponseSetOption, error) {
+	reqres := cli.SetOptionAsync(req)
+	return reqres.Response.GetSetOption(), cli.Error()
 }
 
 func (cli *grpcClient) DeliverTxSync(tx []byte) (*types.ResponseDeliverTx, error) {
@@ -288,17 +285,17 @@ func (cli *grpcClient) CommitSync() (*types.ResponseCommit, error) {
 	return reqres.Response.GetCommit(), cli.Error()
 }
 
-func (cli *grpcClient) InitChainSync(params types.RequestInitChain) error {
-	cli.InitChainAsync(params)
-	return cli.Error()
+func (cli *grpcClient) InitChainSync(params types.RequestInitChain) (*types.ResponseInitChain, error) {
+	reqres := cli.InitChainAsync(params)
+	return reqres.Response.GetInitChain(), cli.Error()
 }
 
-func (cli *grpcClient) BeginBlockSync(params types.RequestBeginBlock) error {
-	cli.BeginBlockAsync(params)
-	return cli.Error()
+func (cli *grpcClient) BeginBlockSync(params types.RequestBeginBlock) (*types.ResponseBeginBlock, error) {
+	reqres := cli.BeginBlockAsync(params)
+	return reqres.Response.GetBeginBlock(), cli.Error()
 }
 
-func (cli *grpcClient) EndBlockSync(height uint64) (*types.ResponseEndBlock, error) {
-	reqres := cli.EndBlockAsync(height)
+func (cli *grpcClient) EndBlockSync(params types.RequestEndBlock) (*types.ResponseEndBlock, error) {
+	reqres := cli.EndBlockAsync(params)
 	return reqres.Response.GetEndBlock(), cli.Error()
 }
diff --git a/client/local_client.go b/client/local_client.go
index 15dda8e6..64bf5fe0 100644
--- a/client/local_client.go
+++ b/client/local_client.go
@@ -53,21 +53,21 @@ func (app *localClient) EchoAsync(msg string) *ReqRes {
 
 func (app *localClient) InfoAsync(req types.RequestInfo) *ReqRes {
 	app.mtx.Lock()
-	resInfo := app.Application.Info(req)
+	res := app.Application.Info(req)
 	app.mtx.Unlock()
 	return app.callback(
 		types.ToRequestInfo(req),
-		types.ToResponseInfo(resInfo),
+		types.ToResponseInfo(res),
 	)
 }
 
-func (app *localClient) SetOptionAsync(key string, value string) *ReqRes {
+func (app *localClient) SetOptionAsync(req types.RequestSetOption) *ReqRes {
 	app.mtx.Lock()
-	log := app.Application.SetOption(key, value)
+	res := app.Application.SetOption(req)
 	app.mtx.Unlock()
 	return app.callback(
-		types.ToRequestSetOption(key, value),
-		types.ToResponseSetOption(log),
+		types.ToRequestSetOption(req),
+		types.ToResponseSetOption(res),
 	)
 }
 
@@ -77,7 +77,7 @@ func (app *localClient) DeliverTxAsync(tx []byte) *ReqRes {
 	app.mtx.Unlock()
 	return app.callback(
 		types.ToRequestDeliverTx(tx),
-		types.ToResponseDeliverTx(res.Code, res.Data, res.Log, res.Tags),
+		types.ToResponseDeliverTx(res),
 	)
 }
 
@@ -87,17 +87,17 @@ func (app *localClient) CheckTxAsync(tx []byte) *ReqRes {
 	app.mtx.Unlock()
 	return app.callback(
 		types.ToRequestCheckTx(tx),
-		types.ToResponseCheckTx(res.Code, res.Data, res.Log),
+		types.ToResponseCheckTx(res),
 	)
 }
 
-func (app *localClient) QueryAsync(reqQuery types.RequestQuery) *ReqRes {
+func (app *localClient) QueryAsync(req types.RequestQuery) *ReqRes {
 	app.mtx.Lock()
-	resQuery := app.Application.Query(reqQuery)
+	res := app.Application.Query(req)
 	app.mtx.Unlock()
 	return app.callback(
-		types.ToRequestQuery(reqQuery),
-		types.ToResponseQuery(resQuery),
+		types.ToRequestQuery(req),
+		types.ToResponseQuery(res),
 	)
 }
 
@@ -107,38 +107,38 @@ func (app *localClient) CommitAsync() *ReqRes {
 	app.mtx.Unlock()
 	return app.callback(
 		types.ToRequestCommit(),
-		types.ToResponseCommit(res.Code, res.Data, res.Log),
+		types.ToResponseCommit(res),
 	)
 }
 
-func (app *localClient) InitChainAsync(params types.RequestInitChain) *ReqRes {
+func (app *localClient) InitChainAsync(req types.RequestInitChain) *ReqRes {
 	app.mtx.Lock()
-	app.Application.InitChain(params)
+	res := app.Application.InitChain(req)
 	reqRes := app.callback(
-		types.ToRequestInitChain(params),
-		types.ToResponseInitChain(),
+		types.ToRequestInitChain(req),
+		types.ToResponseInitChain(res),
 	)
 	app.mtx.Unlock()
 	return reqRes
 }
 
-func (app *localClient) BeginBlockAsync(params types.RequestBeginBlock) *ReqRes {
+func (app *localClient) BeginBlockAsync(req types.RequestBeginBlock) *ReqRes {
 	app.mtx.Lock()
-	app.Application.BeginBlock(params)
+	res := app.Application.BeginBlock(req)
 	app.mtx.Unlock()
 	return app.callback(
-		types.ToRequestBeginBlock(params),
-		types.ToResponseBeginBlock(),
+		types.ToRequestBeginBlock(req),
+		types.ToResponseBeginBlock(res),
 	)
 }
 
-func (app *localClient) EndBlockAsync(height uint64) *ReqRes {
+func (app *localClient) EndBlockAsync(req types.RequestEndBlock) *ReqRes {
 	app.mtx.Lock()
-	resEndBlock := app.Application.EndBlock(height)
+	res := app.Application.EndBlock(req)
 	app.mtx.Unlock()
 	return app.callback(
-		types.ToRequestEndBlock(height),
-		types.ToResponseEndBlock(resEndBlock),
+		types.ToRequestEndBlock(req),
+		types.ToResponseEndBlock(res),
 	)
 }
 
@@ -159,11 +159,11 @@ func (app *localClient) InfoSync(req types.RequestInfo) (*types.ResponseInfo, er
 	return &res, nil
 }
 
-func (app *localClient) SetOptionSync(key string, value string) (log string, err error) {
+func (app *localClient) SetOptionSync(req types.RequestSetOption) (*types.ResponseSetOption, error) {
 	app.mtx.Lock()
-	log = app.Application.SetOption(key, value)
+	res := app.Application.SetOption(req)
 	app.mtx.Unlock()
-	return log, nil
+	return &res, nil
 }
 
 func (app *localClient) DeliverTxSync(tx []byte) (*types.ResponseDeliverTx, error) {
@@ -194,23 +194,23 @@ func (app *localClient) CommitSync() (*types.ResponseCommit, error) {
 	return &res, nil
 }
 
-func (app *localClient) InitChainSync(params types.RequestInitChain) error {
+func (app *localClient) InitChainSync(req types.RequestInitChain) (*types.ResponseInitChain, error) {
 	app.mtx.Lock()
-	app.Application.InitChain(params)
+	res := app.Application.InitChain(req)
 	app.mtx.Unlock()
-	return nil
+	return &res, nil
 }
 
-func (app *localClient) BeginBlockSync(params types.RequestBeginBlock) error {
+func (app *localClient) BeginBlockSync(req types.RequestBeginBlock) (*types.ResponseBeginBlock, error) {
 	app.mtx.Lock()
-	app.Application.BeginBlock(params)
+	res := app.Application.BeginBlock(req)
 	app.mtx.Unlock()
-	return nil
+	return &res, nil
 }
 
-func (app *localClient) EndBlockSync(height uint64) (*types.ResponseEndBlock, error) {
+func (app *localClient) EndBlockSync(req types.RequestEndBlock) (*types.ResponseEndBlock, error) {
 	app.mtx.Lock()
-	res := app.Application.EndBlock(height)
+	res := app.Application.EndBlock(req)
 	app.mtx.Unlock()
 	return &res, nil
 }
diff --git a/client/socket_client.go b/client/socket_client.go
index 716ef451..84377a05 100644
--- a/client/socket_client.go
+++ b/client/socket_client.go
@@ -239,8 +239,8 @@ func (cli *socketClient) InfoAsync(req types.RequestInfo) *ReqRes {
 	return cli.queueRequest(types.ToRequestInfo(req))
 }
 
-func (cli *socketClient) SetOptionAsync(key string, value string) *ReqRes {
-	return cli.queueRequest(types.ToRequestSetOption(key, value))
+func (cli *socketClient) SetOptionAsync(req types.RequestSetOption) *ReqRes {
+	return cli.queueRequest(types.ToRequestSetOption(req))
 }
 
 func (cli *socketClient) DeliverTxAsync(tx []byte) *ReqRes {
@@ -259,16 +259,16 @@ func (cli *socketClient) CommitAsync() *ReqRes {
 	return cli.queueRequest(types.ToRequestCommit())
 }
 
-func (cli *socketClient) InitChainAsync(params types.RequestInitChain) *ReqRes {
-	return cli.queueRequest(types.ToRequestInitChain(params))
+func (cli *socketClient) InitChainAsync(req types.RequestInitChain) *ReqRes {
+	return cli.queueRequest(types.ToRequestInitChain(req))
 }
 
-func (cli *socketClient) BeginBlockAsync(params types.RequestBeginBlock) *ReqRes {
-	return cli.queueRequest(types.ToRequestBeginBlock(params))
+func (cli *socketClient) BeginBlockAsync(req types.RequestBeginBlock) *ReqRes {
+	return cli.queueRequest(types.ToRequestBeginBlock(req))
 }
 
-func (cli *socketClient) EndBlockAsync(height uint64) *ReqRes {
-	return cli.queueRequest(types.ToRequestEndBlock(height))
+func (cli *socketClient) EndBlockAsync(req types.RequestEndBlock) *ReqRes {
+	return cli.queueRequest(types.ToRequestEndBlock(req))
 }
 
 //----------------------------------------
@@ -294,13 +294,10 @@ func (cli *socketClient) InfoSync(req types.RequestInfo) (*types.ResponseInfo, e
 	return reqres.Response.GetInfo(), cli.Error()
 }
 
-func (cli *socketClient) SetOptionSync(key string, value string) (log string, err error) {
-	reqres := cli.queueRequest(types.ToRequestSetOption(key, value))
+func (cli *socketClient) SetOptionSync(req types.RequestSetOption) (*types.ResponseSetOption, error) {
+	reqres := cli.queueRequest(types.ToRequestSetOption(req))
 	cli.FlushSync()
-	if err := cli.Error(); err != nil {
-		return "", err
-	}
-	return reqres.Response.GetSetOption().Log, nil
+	return reqres.Response.GetSetOption(), cli.Error()
 }
 
 func (cli *socketClient) DeliverTxSync(tx []byte) (*types.ResponseDeliverTx, error) {
@@ -327,20 +324,20 @@ func (cli *socketClient) CommitSync() (*types.ResponseCommit, error) {
 	return reqres.Response.GetCommit(), cli.Error()
 }
 
-func (cli *socketClient) InitChainSync(params types.RequestInitChain) error {
-	cli.queueRequest(types.ToRequestInitChain(params))
+func (cli *socketClient) InitChainSync(req types.RequestInitChain) (*types.ResponseInitChain, error) {
+	reqres := cli.queueRequest(types.ToRequestInitChain(req))
 	cli.FlushSync()
-	return cli.Error()
+	return reqres.Response.GetInitChain(), cli.Error()
 }
 
-func (cli *socketClient) BeginBlockSync(params types.RequestBeginBlock) error {
-	cli.queueRequest(types.ToRequestBeginBlock(params))
+func (cli *socketClient) BeginBlockSync(req types.RequestBeginBlock) (*types.ResponseBeginBlock, error) {
+	reqres := cli.queueRequest(types.ToRequestBeginBlock(req))
 	cli.FlushSync()
-	return cli.Error()
+	return reqres.Response.GetBeginBlock(), cli.Error()
 }
 
-func (cli *socketClient) EndBlockSync(height uint64) (*types.ResponseEndBlock, error) {
-	reqres := cli.queueRequest(types.ToRequestEndBlock(height))
+func (cli *socketClient) EndBlockSync(req types.RequestEndBlock) (*types.ResponseEndBlock, error) {
+	reqres := cli.queueRequest(types.ToRequestEndBlock(req))
 	cli.FlushSync()
 	return reqres.Response.GetEndBlock(), cli.Error()
 }
diff --git a/cmd/abci-cli/abci-cli.go b/cmd/abci-cli/abci-cli.go
index e3f0daec..d27bf24b 100644
--- a/cmd/abci-cli/abci-cli.go
+++ b/cmd/abci-cli/abci-cli.go
@@ -355,12 +355,13 @@ func cmdInfo(cmd *cobra.Command, args []string) error {
 
 // Set an option on the application
 func cmdSetOption(cmd *cobra.Command, args []string) error {
-	resLog, err := client.SetOptionSync(args[0], args[1])
+	key, val := args[0], args[1]
+	res, err := client.SetOptionSync(types.RequestSetOption{key, val})
 	if err != nil {
 		return err
 	}
 	printResponse(cmd, args, response{
-		Log: resLog,
+		Log: res.Log,
 	})
 	return nil
 }
diff --git a/example/block_aware/block_aware_app.go b/example/block_aware/block_aware_app.go
deleted file mode 100644
index 8a031da2..00000000
--- a/example/block_aware/block_aware_app.go
+++ /dev/null
@@ -1,65 +0,0 @@
-package main
-
-import (
-	"flag"
-	"os"
-
-	"github.com/tendermint/abci/server"
-	"github.com/tendermint/abci/types"
-	cmn "github.com/tendermint/tmlibs/common"
-	"github.com/tendermint/tmlibs/log"
-)
-
-func main() {
-
-	addrPtr := flag.String("addr", "tcp://0.0.0.0:46658", "Listen address")
-	abciPtr := flag.String("abci", "socket", "socket | grpc")
-	flag.Parse()
-
-	logger := log.NewTMLogger(log.NewSyncWriter(os.Stdout))
-
-	// Start the listener
-	srv, err := server.NewServer(*addrPtr, *abciPtr, NewChainAwareApplication())
-	if err != nil {
-		logger.Error(err.Error())
-		os.Exit(1)
-	}
-	srv.SetLogger(logger.With("module", "abci-server"))
-	if _, err := srv.Start(); err != nil {
-		logger.Error(err.Error())
-		os.Exit(1)
-	}
-
-	// Wait forever
-	cmn.TrapSignal(func() {
-		// Cleanup
-		srv.Stop()
-	})
-
-}
-
-type ChainAwareApplication struct {
-	types.BaseApplication
-
-	beginCount int
-	endCount   int
-}
-
-func NewChainAwareApplication() *ChainAwareApplication {
-	return &ChainAwareApplication{}
-}
-
-func (app *ChainAwareApplication) Query(reqQuery types.RequestQuery) (resQuery types.ResponseQuery) {
-	return types.ResponseQuery{
-		Value: []byte(cmn.Fmt("%d,%d", app.beginCount, app.endCount)),
-	}
-}
-
-func (app *ChainAwareApplication) BeginBlock(reqBeginBlock types.RequestBeginBlock) {
-	app.beginCount++
-}
-
-func (app *ChainAwareApplication) EndBlock(height uint64) (resEndBlock types.ResponseEndBlock) {
-	app.endCount++
-	return
-}
diff --git a/example/block_aware/block_aware_test.go b/example/block_aware/block_aware_test.go
deleted file mode 100644
index 2777ce1a..00000000
--- a/example/block_aware/block_aware_test.go
+++ /dev/null
@@ -1,57 +0,0 @@
-package main
-
-import (
-	"strconv"
-	"strings"
-	"testing"
-
-	abcicli "github.com/tendermint/abci/client"
-	"github.com/tendermint/abci/server"
-	"github.com/tendermint/abci/types"
-	"github.com/tendermint/tmlibs/log"
-)
-
-func TestChainAware(t *testing.T) {
-	app := NewChainAwareApplication()
-
-	// Start the listener
-	srv, err := server.NewServer("unix://test.sock", "socket", app)
-	if err != nil {
-		t.Fatal(err)
-	}
-	srv.SetLogger(log.TestingLogger().With("module", "abci-server"))
-	if _, err := srv.Start(); err != nil {
-		t.Fatal(err.Error())
-	}
-	defer srv.Stop()
-
-	// Connect to the socket
-	client := abcicli.NewSocketClient("unix://test.sock", false)
-	client.SetLogger(log.TestingLogger().With("module", "abci-client"))
-	if _, err := client.Start(); err != nil {
-		t.Fatalf("Error starting socket client: %v", err.Error())
-	}
-	defer client.Stop()
-
-	n := uint64(5)
-	hash := []byte("fake block hash")
-	header := &types.Header{}
-	for i := uint64(0); i < n; i++ {
-		client.BeginBlockSync(types.RequestBeginBlock{hash, header})
-		client.EndBlockSync(i)
-		client.CommitSync()
-	}
-
-	r := app.Query(types.RequestQuery{})
-	spl := strings.Split(string(r.Value), ",")
-	if len(spl) != 2 {
-		t.Fatal("expected %d,%d ; got %s", n, n, string(r.Value))
-	}
-	beginCount, _ := strconv.Atoi(spl[0])
-	endCount, _ := strconv.Atoi(spl[1])
-	if uint64(beginCount) != n {
-		t.Fatalf("expected beginCount of %d, got %d", n, beginCount)
-	} else if uint64(endCount) != n {
-		t.Fatalf("expected endCount of %d, got %d", n, endCount)
-	}
-}
diff --git a/example/counter/counter.go b/example/counter/counter.go
index 65cac4a0..a7b09027 100644
--- a/example/counter/counter.go
+++ b/example/counter/counter.go
@@ -24,11 +24,12 @@ func (app *CounterApplication) Info(req types.RequestInfo) types.ResponseInfo {
 	return types.ResponseInfo{Data: cmn.Fmt("{\"hashes\":%v,\"txs\":%v}", app.hashCount, app.txCount)}
 }
 
-func (app *CounterApplication) SetOption(key string, value string) (log string) {
+func (app *CounterApplication) SetOption(req types.RequestSetOption) types.ResponseSetOption {
+	key, value := req.Key, req.Value
 	if key == "serial" && value == "on" {
 		app.serial = true
 	}
-	return ""
+	return types.ResponseSetOption{}
 }
 
 func (app *CounterApplication) DeliverTx(tx []byte) types.ResponseDeliverTx {
diff --git a/example/dummy/dummy.go b/example/dummy/dummy.go
index a4edacac..65d524cf 100644
--- a/example/dummy/dummy.go
+++ b/example/dummy/dummy.go
@@ -10,6 +10,8 @@ import (
 	dbm "github.com/tendermint/tmlibs/db"
 )
 
+var _ types.Application = (*DummyApplication)(nil)
+
 type DummyApplication struct {
 	types.BaseApplication
 
diff --git a/example/dummy/dummy_test.go b/example/dummy/dummy_test.go
index 798da720..b7aef6a8 100644
--- a/example/dummy/dummy_test.go
+++ b/example/dummy/dummy_test.go
@@ -93,7 +93,7 @@ func TestPersistentDummyInfo(t *testing.T) {
 		Height: uint64(height),
 	}
 	dummy.BeginBlock(types.RequestBeginBlock{hash, header})
-	dummy.EndBlock(height)
+	dummy.EndBlock(types.RequestEndBlock{header.Height})
 	dummy.Commit()
 
 	resInfo = dummy.Info(types.RequestInfo{})
@@ -182,7 +182,7 @@ func makeApplyBlock(t *testing.T, dummy types.Application, heightInt int, diff [
 			t.Fatal(r)
 		}
 	}
-	resEndBlock := dummy.EndBlock(height)
+	resEndBlock := dummy.EndBlock(types.RequestEndBlock{header.Height})
 	dummy.Commit()
 
 	valsEqual(t, diff, resEndBlock.Diffs)
diff --git a/example/dummy/persistent_dummy.go b/example/dummy/persistent_dummy.go
index 8fa11282..ed284529 100644
--- a/example/dummy/persistent_dummy.go
+++ b/example/dummy/persistent_dummy.go
@@ -21,6 +21,8 @@ const (
 
 //-----------------------------------------
 
+var _ types.Application = (*PersistentDummyApplication)(nil)
+
 type PersistentDummyApplication struct {
 	app *DummyApplication
 
@@ -50,15 +52,15 @@ func (app *PersistentDummyApplication) SetLogger(l log.Logger) {
 	app.logger = l
 }
 
-func (app *PersistentDummyApplication) Info(req types.RequestInfo) (resInfo types.ResponseInfo) {
-	resInfo = app.app.Info(req)
-	resInfo.LastBlockHeight = app.app.state.LatestVersion()
-	resInfo.LastBlockAppHash = app.app.state.Hash()
-	return resInfo
+func (app *PersistentDummyApplication) Info(req types.RequestInfo) types.ResponseInfo {
+	res := app.app.Info(req)
+	res.LastBlockHeight = app.app.state.LatestVersion()
+	res.LastBlockAppHash = app.app.state.Hash()
+	return res
 }
 
-func (app *PersistentDummyApplication) SetOption(key string, value string) (log string) {
-	return app.app.SetOption(key, value)
+func (app *PersistentDummyApplication) SetOption(req types.RequestSetOption) types.ResponseSetOption {
+	return app.app.SetOption(req)
 }
 
 // tx is either "val:pubkey/power" or "key=value" or just arbitrary bytes
@@ -102,23 +104,25 @@ func (app *PersistentDummyApplication) Query(reqQuery types.RequestQuery) types.
 }
 
 // Save the validators in the merkle tree
-func (app *PersistentDummyApplication) InitChain(params types.RequestInitChain) {
-	for _, v := range params.Validators {
+func (app *PersistentDummyApplication) InitChain(req types.RequestInitChain) types.ResponseInitChain {
+	for _, v := range req.Validators {
 		r := app.updateValidator(v)
 		if r.IsErr() {
 			app.logger.Error("Error updating validators", "r", r)
 		}
 	}
+	return types.ResponseInitChain{}
 }
 
 // Track the block hash and header information
-func (app *PersistentDummyApplication) BeginBlock(params types.RequestBeginBlock) {
+func (app *PersistentDummyApplication) BeginBlock(req types.RequestBeginBlock) types.ResponseBeginBlock {
 	// reset valset changes
 	app.changes = make([]*types.Validator, 0)
+	return types.ResponseBeginBlock{}
 }
 
 // Update the validator set
-func (app *PersistentDummyApplication) EndBlock(height uint64) (resEndBlock types.ResponseEndBlock) {
+func (app *PersistentDummyApplication) EndBlock(req types.RequestEndBlock) types.ResponseEndBlock {
 	return types.ResponseEndBlock{Diffs: app.changes}
 }
 
diff --git a/server/socket_server.go b/server/socket_server.go
index 68a21322..c88180d4 100644
--- a/server/socket_server.go
+++ b/server/socket_server.go
@@ -168,33 +168,32 @@ func (s *SocketServer) handleRequest(req *types.Request, responses chan<- *types
 	case *types.Request_Flush:
 		responses <- types.ToResponseFlush()
 	case *types.Request_Info:
-		resInfo := s.app.Info(*r.Info)
-		responses <- types.ToResponseInfo(resInfo)
+		res := s.app.Info(*r.Info)
+		responses <- types.ToResponseInfo(res)
 	case *types.Request_SetOption:
-		so := r.SetOption
-		logStr := s.app.SetOption(so.Key, so.Value)
-		responses <- types.ToResponseSetOption(logStr)
+		res := s.app.SetOption(*r.SetOption)
+		responses <- types.ToResponseSetOption(res)
 	case *types.Request_DeliverTx:
 		res := s.app.DeliverTx(r.DeliverTx.Tx)
-		responses <- types.ToResponseDeliverTx(res.Code, res.Data, res.Log, res.Tags)
+		responses <- types.ToResponseDeliverTx(res)
 	case *types.Request_CheckTx:
 		res := s.app.CheckTx(r.CheckTx.Tx)
-		responses <- types.ToResponseCheckTx(res.Code, res.Data, res.Log)
+		responses <- types.ToResponseCheckTx(res)
 	case *types.Request_Commit:
 		res := s.app.Commit()
-		responses <- types.ToResponseCommit(res.Code, res.Data, res.Log)
+		responses <- types.ToResponseCommit(res)
 	case *types.Request_Query:
-		resQuery := s.app.Query(*r.Query)
-		responses <- types.ToResponseQuery(resQuery)
+		res := s.app.Query(*r.Query)
+		responses <- types.ToResponseQuery(res)
 	case *types.Request_InitChain:
-		s.app.InitChain(*r.InitChain)
-		responses <- types.ToResponseInitChain()
+		res := s.app.InitChain(*r.InitChain)
+		responses <- types.ToResponseInitChain(res)
 	case *types.Request_BeginBlock:
-		s.app.BeginBlock(*r.BeginBlock)
-		responses <- types.ToResponseBeginBlock()
+		res := s.app.BeginBlock(*r.BeginBlock)
+		responses <- types.ToResponseBeginBlock(res)
 	case *types.Request_EndBlock:
-		resEndBlock := s.app.EndBlock(r.EndBlock.Height)
-		responses <- types.ToResponseEndBlock(resEndBlock)
+		res := s.app.EndBlock(*r.EndBlock)
+		responses <- types.ToResponseEndBlock(res)
 	default:
 		responses <- types.ToResponseException("Unknown request")
 	}
diff --git a/types/application.go b/types/application.go
index ed9b0d20..c36e58f0 100644
--- a/types/application.go
+++ b/types/application.go
@@ -5,22 +5,24 @@ import (
 )
 
 // Application is an interface that enables any finite, deterministic state machine
-// to be driven by a blockchain-based replication engine via the ABCI
+// to be driven by a blockchain-based replication engine via the ABCI.
+// All methods take a RequestXxx argument and return a ResponseXxx argument,
+// except CheckTx/DeliverTx, which take `tx []byte`, and `Commit`, which takes nothing.
 type Application interface {
 	// Info/Query Connection
-	Info(RequestInfo) ResponseInfo                   // Return application info
-	SetOption(key string, value string) (log string) // Set application option
-	Query(RequestQuery) ResponseQuery                // Query for state
+	Info(RequestInfo) ResponseInfo                // Return application info
+	SetOption(RequestSetOption) ResponseSetOption // Set application option
+	Query(RequestQuery) ResponseQuery             // Query for state
 
 	// Mempool Connection
 	CheckTx(tx []byte) ResponseCheckTx // Validate a tx for the mempool
 
 	// Consensus Connection
-	InitChain(RequestInitChain)              // Initialize blockchain with validators and other info from TendermintCore
-	BeginBlock(RequestBeginBlock)            // Signals the beginning of a block
-	DeliverTx(tx []byte) ResponseDeliverTx   // Deliver a tx for full processing
-	EndBlock(height uint64) ResponseEndBlock // Signals the end of a block, returns changes to the validator set
-	Commit() ResponseCommit                  // Commit the state and return the application Merkle root hash
+	InitChain(RequestInitChain) ResponseInitChain    // Initialize blockchain with validators and other info from TendermintCore
+	BeginBlock(RequestBeginBlock) ResponseBeginBlock // Signals the beginning of a block
+	DeliverTx(tx []byte) ResponseDeliverTx           // Deliver a tx for full processing
+	EndBlock(RequestEndBlock) ResponseEndBlock       // Signals the end of a block, returns changes to the validator set
+	Commit() ResponseCommit                          // Commit the state and return the application Merkle root hash
 }
 
 //------------------------------------
@@ -48,7 +50,8 @@ func (app *GRPCApplication) Info(ctx context.Context, req *RequestInfo) (*Respon
 }
 
 func (app *GRPCApplication) SetOption(ctx context.Context, req *RequestSetOption) (*ResponseSetOption, error) {
-	return &ResponseSetOption{app.app.SetOption(req.Key, req.Value)}, nil
+	resSetOption := app.app.SetOption(*req)
+	return &resSetOption, nil
 }
 
 func (app *GRPCApplication) DeliverTx(ctx context.Context, req *RequestDeliverTx) (*ResponseDeliverTx, error) {
@@ -72,16 +75,16 @@ func (app *GRPCApplication) Commit(ctx context.Context, req *RequestCommit) (*Re
 }
 
 func (app *GRPCApplication) InitChain(ctx context.Context, req *RequestInitChain) (*ResponseInitChain, error) {
-	app.app.InitChain(*req)
-	return &ResponseInitChain{}, nil // NOTE: empty return
+	resInitChain := app.app.InitChain(*req)
+	return &resInitChain, nil
 }
 
 func (app *GRPCApplication) BeginBlock(ctx context.Context, req *RequestBeginBlock) (*ResponseBeginBlock, error) {
-	app.app.BeginBlock(*req)
-	return &ResponseBeginBlock{}, nil // NOTE: empty return
+	resBeginBlock := app.app.BeginBlock(*req)
+	return &resBeginBlock, nil
 }
 
 func (app *GRPCApplication) EndBlock(ctx context.Context, req *RequestEndBlock) (*ResponseEndBlock, error) {
-	resEndBlock := app.app.EndBlock(req.Height)
+	resEndBlock := app.app.EndBlock(*req)
 	return &resEndBlock, nil
 }
diff --git a/types/base_app.go b/types/base_app.go
index 0086685b..404678e9 100644
--- a/types/base_app.go
+++ b/types/base_app.go
@@ -11,8 +11,8 @@ func (BaseApplication) Info(req RequestInfo) ResponseInfo {
 	return ResponseInfo{}
 }
 
-func (BaseApplication) SetOption(key string, value string) (log string) {
-	return ""
+func (BaseApplication) SetOption(req RequestSetOption) ResponseSetOption {
+	return ResponseSetOption{}
 }
 
 func (BaseApplication) DeliverTx(tx []byte) ResponseDeliverTx {
@@ -31,12 +31,14 @@ func (BaseApplication) Query(req RequestQuery) ResponseQuery {
 	return ResponseQuery{Code: CodeType_OK}
 }
 
-func (BaseApplication) InitChain(req RequestInitChain) {
+func (BaseApplication) InitChain(req RequestInitChain) ResponseInitChain {
+	return ResponseInitChain{}
 }
 
-func (BaseApplication) BeginBlock(req RequestBeginBlock) {
+func (BaseApplication) BeginBlock(req RequestBeginBlock) ResponseBeginBlock {
+	return ResponseBeginBlock{}
 }
 
-func (BaseApplication) EndBlock(height uint64) ResponseEndBlock {
+func (BaseApplication) EndBlock(req RequestEndBlock) ResponseEndBlock {
 	return ResponseEndBlock{}
 }
diff --git a/types/messages.go b/types/messages.go
index 298f17ba..77ad538e 100644
--- a/types/messages.go
+++ b/types/messages.go
@@ -25,21 +25,21 @@ func ToRequestInfo(req RequestInfo) *Request {
 	}
 }
 
-func ToRequestSetOption(key string, value string) *Request {
+func ToRequestSetOption(req RequestSetOption) *Request {
 	return &Request{
-		Value: &Request_SetOption{&RequestSetOption{key, value}},
+		Value: &Request_SetOption{&req},
 	}
 }
 
-func ToRequestDeliverTx(txBytes []byte) *Request {
+func ToRequestDeliverTx(tx []byte) *Request {
 	return &Request{
-		Value: &Request_DeliverTx{&RequestDeliverTx{txBytes}},
+		Value: &Request_DeliverTx{&RequestDeliverTx{tx}},
 	}
 }
 
-func ToRequestCheckTx(txBytes []byte) *Request {
+func ToRequestCheckTx(tx []byte) *Request {
 	return &Request{
-		Value: &Request_CheckTx{&RequestCheckTx{txBytes}},
+		Value: &Request_CheckTx{&RequestCheckTx{tx}},
 	}
 }
 
@@ -67,9 +67,9 @@ func ToRequestBeginBlock(req RequestBeginBlock) *Request {
 	}
 }
 
-func ToRequestEndBlock(height uint64) *Request {
+func ToRequestEndBlock(req RequestEndBlock) *Request {
 	return &Request{
-		Value: &Request_EndBlock{&RequestEndBlock{height}},
+		Value: &Request_EndBlock{&req},
 	}
 }
 
@@ -93,57 +93,57 @@ func ToResponseFlush() *Response {
 	}
 }
 
-func ToResponseInfo(resInfo ResponseInfo) *Response {
+func ToResponseInfo(res ResponseInfo) *Response {
 	return &Response{
-		Value: &Response_Info{&resInfo},
+		Value: &Response_Info{&res},
 	}
 }
 
-func ToResponseSetOption(log string) *Response {
+func ToResponseSetOption(res ResponseSetOption) *Response {
 	return &Response{
-		Value: &Response_SetOption{&ResponseSetOption{log}},
+		Value: &Response_SetOption{&res},
 	}
 }
 
-func ToResponseDeliverTx(code CodeType, data []byte, log string, tags []*KVPair) *Response {
+func ToResponseDeliverTx(res ResponseDeliverTx) *Response {
 	return &Response{
-		Value: &Response_DeliverTx{&ResponseDeliverTx{code, data, log, tags}},
+		Value: &Response_DeliverTx{&res},
 	}
 }
 
-func ToResponseCheckTx(code CodeType, data []byte, log string) *Response {
+func ToResponseCheckTx(res ResponseCheckTx) *Response {
 	return &Response{
-		Value: &Response_CheckTx{&ResponseCheckTx{code, data, log}},
+		Value: &Response_CheckTx{&res},
 	}
 }
 
-func ToResponseCommit(code CodeType, data []byte, log string) *Response {
+func ToResponseCommit(res ResponseCommit) *Response {
 	return &Response{
-		Value: &Response_Commit{&ResponseCommit{code, data, log}},
+		Value: &Response_Commit{&res},
 	}
 }
 
-func ToResponseQuery(resQuery ResponseQuery) *Response {
+func ToResponseQuery(res ResponseQuery) *Response {
 	return &Response{
-		Value: &Response_Query{&resQuery},
+		Value: &Response_Query{&res},
 	}
 }
 
-func ToResponseInitChain() *Response {
+func ToResponseInitChain(res ResponseInitChain) *Response {
 	return &Response{
-		Value: &Response_InitChain{&ResponseInitChain{}},
+		Value: &Response_InitChain{&res},
 	}
 }
 
-func ToResponseBeginBlock() *Response {
+func ToResponseBeginBlock(res ResponseBeginBlock) *Response {
 	return &Response{
-		Value: &Response_BeginBlock{&ResponseBeginBlock{}},
+		Value: &Response_BeginBlock{&res},
 	}
 }
 
-func ToResponseEndBlock(resEndBlock ResponseEndBlock) *Response {
+func ToResponseEndBlock(res ResponseEndBlock) *Response {
 	return &Response{
-		Value: &Response_EndBlock{&resEndBlock},
+		Value: &Response_EndBlock{&res},
 	}
 }