diff --git a/CMakeLists.txt b/CMakeLists.txt
index 02c930abc..c258f133d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -23,10 +23,11 @@ file(GLOB GBA_SV_SRC ${CMAKE_SOURCE_DIR}/src/gba/supervisor/*.c)
 file(GLOB UTIL_SRC ${CMAKE_SOURCE_DIR}/src/util/*.[cSs])
 file(GLOB VFS_SRC ${CMAKE_SOURCE_DIR}/src/util/vfs/*.c)
 file(GLOB RENDERER_SRC ${CMAKE_SOURCE_DIR}/src/gba/renderers/video-software.c)
+file(GLOB SIO_SRC ${CMAKE_SOURCE_DIR}/src/gba/sio/lockstep.c)
 file(GLOB THIRD_PARTY_SRC ${CMAKE_SOURCE_DIR}/src/third-party/inih/*.c)
 list(APPEND UTIL_SRC ${CMAKE_SOURCE_DIR}/src/platform/commandline.c)
 source_group("ARM core" FILES ${ARM_SRC})
-source_group("GBA board" FILES ${GBA_SRC} ${RENDERER_SRC})
+source_group("GBA board" FILES ${GBA_SRC} ${RENDERER_SRC} ${SIO_SRC})
 source_group("GBA supervisor" FILES ${GBA_SV_SRC} ${GBA_RR_SRC})
 source_group("Utilities" FILES ${UTIL_SRC} ${VFS_SRC}})
 include_directories(${CMAKE_SOURCE_DIR}/src/arm)
@@ -296,6 +297,7 @@ set(CORE_SRC
 	${GBA_SV_SRC}
 	${DEBUGGER_SRC}
 	${RENDERER_SRC}
+	${SIO_SRC}
 	${UTIL_SRC}
 	${VFS_SRC}
 	${OS_SRC}
diff --git a/src/gba/sio.h b/src/gba/sio.h
index 030218cc8..61e979385 100644
--- a/src/gba/sio.h
+++ b/src/gba/sio.h
@@ -30,11 +30,11 @@ struct GBASIO;
 struct GBASIODriver {
 	struct GBASIO* p;
 
-	int (*init)(struct GBASIODriver* driver);
+	bool (*init)(struct GBASIODriver* driver);
 	void (*deinit)(struct GBASIODriver* driver);
-	int (*load)(struct GBASIODriver* driver);
-	int (*unload)(struct GBASIODriver* driver);
-	int (*writeRegister)(struct GBASIODriver* driver, uint32_t address, uint16_t value);
+	bool (*load)(struct GBASIODriver* driver);
+	bool (*unload)(struct GBASIODriver* driver);
+	uint16_t (*writeRegister)(struct GBASIODriver* driver, uint32_t address, uint16_t value);
 	int32_t (*processEvents)(struct GBASIODriver* driver, int32_t cycles);
 };
 
diff --git a/src/gba/sio/lockstep.c b/src/gba/sio/lockstep.c
new file mode 100644
index 000000000..842db4571
--- /dev/null
+++ b/src/gba/sio/lockstep.c
@@ -0,0 +1,193 @@
+/* Copyright (c) 2013-2015 Jeffrey Pfau
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+#include "lockstep.h"
+
+#include "gba/gba.h"
+#include "gba/io.h"
+
+#define LOCKSTEP_INCREMENT 2048
+
+static bool GBASIOLockstepNodeInit(struct GBASIODriver* driver);
+static void GBASIOLockstepNodeDeinit(struct GBASIODriver* driver);
+static bool GBASIOLockstepNodeLoad(struct GBASIODriver* driver);
+static bool GBASIOLockstepNodeUnload(struct GBASIODriver* driver);
+static uint16_t GBASIOLockstepNodeWriteRegister(struct GBASIODriver* driver, uint32_t address, uint16_t value);
+static int32_t GBASIOLockstepNodeProcessEvents(struct GBASIODriver* driver, int32_t cycles);
+
+void GBASIOLockstepInit(struct GBASIOLockstep* lockstep) {
+	lockstep->players[0] = 0;
+	lockstep->players[1] = 0;
+	lockstep->players[2] = 0;
+	lockstep->players[3] = 0;
+	lockstep->multiRecv[0] = 0xFFFF;
+	lockstep->multiRecv[1] = 0xFFFF;
+	lockstep->multiRecv[2] = 0xFFFF;
+	lockstep->multiRecv[3] = 0xFFFF;
+	lockstep->attached = 0;
+	lockstep->loaded = 0;
+	lockstep->transferActive = false;
+	lockstep->waiting = 0;
+	lockstep->nextEvent = LOCKSTEP_INCREMENT;
+	ConditionInit(&lockstep->barrier);
+	MutexInit(&lockstep->mutex);
+}
+
+void GBASIOLockstepDeinit(struct GBASIOLockstep* lockstep) {
+	ConditionDeinit(&lockstep->barrier);
+	MutexDeinit(&lockstep->mutex);
+}
+
+void GBASIOLockstepNodeCreate(struct GBASIOLockstepNode* node) {
+	node->d.init = GBASIOLockstepNodeInit;
+	node->d.deinit = GBASIOLockstepNodeDeinit;
+	node->d.load = GBASIOLockstepNodeLoad;
+	node->d.unload = GBASIOLockstepNodeUnload;
+	node->d.writeRegister = GBASIOLockstepNodeWriteRegister;
+	node->d.processEvents = GBASIOLockstepNodeProcessEvents;
+}
+
+bool GBASIOLockstepAttachNode(struct GBASIOLockstep* lockstep, struct GBASIOLockstepNode* node) {
+	if (lockstep->attached == MAX_GBAS) {
+		return false;
+	}
+	lockstep->players[lockstep->attached] = node;
+	node->p = lockstep;
+	node->id = lockstep->attached;
+	++lockstep->attached;
+	return true;
+}
+
+void GBASIOLockstepDetachNode(struct GBASIOLockstep* lockstep, struct GBASIOLockstepNode* node) {
+	if (lockstep->attached == 0) {
+		return;
+	}
+	int i;
+	for (i = 0; i < lockstep->attached; ++i) {
+		if (lockstep->players[i] != node) {
+			continue;
+		}
+		for (++i; i < lockstep->attached; ++i) {
+			lockstep->players[i - 1] = lockstep->players[i];
+			lockstep->players[i - 1]->id = i - 1;
+		}
+		--lockstep->attached;
+		break;
+	}
+}
+
+bool GBASIOLockstepNodeInit(struct GBASIODriver* driver) {
+	struct GBASIOLockstepNode* node = (struct GBASIOLockstepNode*) driver;
+	node->nextEvent = LOCKSTEP_INCREMENT;
+	node->d.p->multiplayerControl.slave = node->id > 0;
+	return true;
+}
+
+void GBASIOLockstepNodeDeinit(struct GBASIODriver* driver) {
+	UNUSED(driver);
+}
+
+bool GBASIOLockstepNodeLoad(struct GBASIODriver* driver) {
+	struct GBASIOLockstepNode* node = (struct GBASIOLockstepNode*) driver;
+	node->state = LOCKSTEP_IDLE;
+	MutexLock(&node->p->mutex);
+	++node->p->loaded;
+	node->d.p->rcnt |= 3;
+	if (node->id) {
+		node->d.p->rcnt |= 4;
+		node->d.p->multiplayerControl.slave = 1;
+	}
+	MutexUnlock(&node->p->mutex);
+	return true;
+}
+
+bool GBASIOLockstepNodeUnload(struct GBASIODriver* driver) {
+	struct GBASIOLockstepNode* node = (struct GBASIOLockstepNode*) driver;
+	MutexLock(&node->p->mutex);
+	--node->p->loaded;
+	ConditionWake(&node->p->barrier);
+	MutexUnlock(&node->p->mutex);
+	return true;
+}
+
+static uint16_t GBASIOLockstepNodeWriteRegister(struct GBASIODriver* driver, uint32_t address, uint16_t value) {
+	struct GBASIOLockstepNode* node = (struct GBASIOLockstepNode*) driver;
+	if (address == REG_SIOCNT) {
+		if (value & 0x0080) {
+			value &= ~0x0080;
+			if (!node->id) {
+				MutexLock(&node->p->mutex);
+				node->p->transferActive = true;
+				node->p->transferCycles = GBASIOCyclesPerTransfer[node->d.p->multiplayerControl.baud][node->p->attached - 1];
+				MutexUnlock(&node->p->mutex);
+			}
+		}
+		value &= 0xFF03;
+		value |= driver->p->siocnt & 0x007C;
+	}
+	return value;
+}
+
+static int32_t GBASIOLockstepNodeProcessEvents(struct GBASIODriver* driver, int32_t cycles) {
+	struct GBASIOLockstepNode* node = (struct GBASIOLockstepNode*) driver;
+	node->nextEvent -= cycles;
+	while (node->nextEvent <= 0) {
+		MutexLock(&node->p->mutex);
+		++node->p->waiting;
+		if (node->p->waiting < node->p->loaded) {
+			ConditionWait(&node->p->barrier, &node->p->mutex);
+		} else {
+			if (node->p->transferActive) {
+				node->p->transferCycles -= node->p->nextEvent;
+				if (node->p->transferCycles > 0) {
+					if (node->p->transferCycles < LOCKSTEP_INCREMENT) {
+						node->p->nextEvent = node->p->transferCycles;
+					}
+				} else {
+					node->p->nextEvent = LOCKSTEP_INCREMENT;
+					node->p->transferActive = false;
+					int i;
+					for (i = 0; i < node->p->attached; ++i) {
+						node->p->multiRecv[i] = node->p->players[i]->multiSend;
+						node->p->players[i]->state = LOCKSTEP_FINISHED;
+					}
+					for (; i < MAX_GBAS; ++i) {
+						node->p->multiRecv[i] = 0xFFFF;
+					}
+				}
+			}
+			node->p->waiting = 0;
+			ConditionWake(&node->p->barrier);
+		}
+		if (node->state == LOCKSTEP_FINISHED) {
+			node->d.p->p->memory.io[REG_SIOMULTI0 >> 1] = node->p->multiRecv[0];
+			node->d.p->p->memory.io[REG_SIOMULTI1 >> 1] = node->p->multiRecv[1];
+			node->d.p->p->memory.io[REG_SIOMULTI2 >> 1] = node->p->multiRecv[2];
+			node->d.p->p->memory.io[REG_SIOMULTI3 >> 1] = node->p->multiRecv[3];
+			node->d.p->rcnt |= 1;
+			node->state = LOCKSTEP_IDLE;
+			if (node->d.p->multiplayerControl.irq) {
+				GBARaiseIRQ(node->d.p->p, IRQ_SIO);
+			}
+			node->d.p->multiplayerControl.id = node->id;
+			node->d.p->multiplayerControl.busy = 0;
+		} else if (node->state == LOCKSTEP_IDLE && node->p->transferActive) {
+			node->state = LOCKSTEP_STARTED;
+			node->d.p->p->memory.io[REG_SIOMULTI0 >> 1] = 0xFFFF;
+			node->d.p->p->memory.io[REG_SIOMULTI1 >> 1] = 0xFFFF;
+			node->d.p->p->memory.io[REG_SIOMULTI2 >> 1] = 0xFFFF;
+			node->d.p->p->memory.io[REG_SIOMULTI3 >> 1] = 0xFFFF;
+			node->d.p->rcnt &= ~1;
+			node->multiSend = node->d.p->p->memory.io[REG_SIOMLT_SEND >> 1];
+			if (node->id) {
+				node->d.p->multiplayerControl.busy = 1;
+			}
+		}
+		node->d.p->multiplayerControl.ready = node->p->loaded == node->p->attached;
+		node->nextEvent += node->p->nextEvent;
+		MutexUnlock(&node->p->mutex);
+	}
+	return node->nextEvent;
+}
diff --git a/src/gba/sio/lockstep.h b/src/gba/sio/lockstep.h
new file mode 100644
index 000000000..3b4c5979e
--- /dev/null
+++ b/src/gba/sio/lockstep.h
@@ -0,0 +1,52 @@
+/* Copyright (c) 2013-2015 Jeffrey Pfau
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+#ifndef SIO_LOCKSTEP_H
+#define SIO_LOCKSTEP_H
+
+#include "gba/sio.h"
+
+#include "util/threading.h"
+
+enum LockstepState {
+	LOCKSTEP_IDLE = 0,
+	LOCKSTEP_STARTED = 1,
+	LOCKSTEP_FINISHED = 2
+};
+
+struct GBASIOLockstep {
+	struct GBASIOLockstepNode* players[MAX_GBAS];
+	int attached;
+	int loaded;
+
+	uint16_t multiRecv[MAX_GBAS];
+	bool transferActive;
+	int32_t transferCycles;
+	int32_t nextEvent;
+
+	int waiting;
+	Mutex mutex;
+	Condition barrier;
+};
+
+struct GBASIOLockstepNode {
+	struct GBASIODriver d;
+	struct GBASIOLockstep* p;
+
+	int32_t nextEvent;
+	uint16_t multiSend;
+	enum LockstepState state;
+	int id;
+};
+
+void GBASIOLockstepInit(struct GBASIOLockstep*);
+void GBASIOLockstepDeinit(struct GBASIOLockstep*);
+
+void GBASIOLockstepNodeCreate(struct GBASIOLockstepNode*);
+
+bool GBASIOLockstepAttachNode(struct GBASIOLockstep*, struct GBASIOLockstepNode*);
+void GBASIOLockstepDetachNode(struct GBASIOLockstep*, struct GBASIOLockstepNode*);
+
+#endif
diff --git a/src/platform/qt/CMakeLists.txt b/src/platform/qt/CMakeLists.txt
index 4b0900be6..69cf68712 100644
--- a/src/platform/qt/CMakeLists.txt
+++ b/src/platform/qt/CMakeLists.txt
@@ -51,6 +51,7 @@ set(SOURCE_FILES
 	KeyEditor.cpp
 	LoadSaveState.cpp
 	LogView.cpp
+	MultiplayerController.cpp
 	OverrideView.cpp
 	SavestateButton.cpp
 	SensorView.cpp
diff --git a/src/platform/qt/ConfigController.cpp b/src/platform/qt/ConfigController.cpp
index c33190a65..ba21ff288 100644
--- a/src/platform/qt/ConfigController.cpp
+++ b/src/platform/qt/ConfigController.cpp
@@ -23,8 +23,11 @@ ConfigOption::ConfigOption(QObject* parent)
 {
 }
 
-void ConfigOption::connect(std::function<void(const QVariant&)> slot) {
-	m_slot = slot;
+void ConfigOption::connect(std::function<void(const QVariant&)> slot, QObject* parent) {
+	m_slots[parent] = slot;
+	QObject::connect(parent, &QAction::destroyed, [this, slot, parent]() {
+		m_slots.remove(parent);
+	});
 }
 
 QAction* ConfigOption::addValue(const QString& text, const QVariant& value, QMenu* parent) {
@@ -33,6 +36,9 @@ QAction* ConfigOption::addValue(const QString& text, const QVariant& value, QMen
 	QObject::connect(action, &QAction::triggered, [this, value]() {
 		emit valueChanged(value);
 	});
+	QObject::connect(parent, &QAction::destroyed, [this, action, value]() {
+		m_actions.removeAll(qMakePair(action, value));
+	});
 	parent->addAction(action);
 	m_actions.append(qMakePair(action, value));
 	return action;
@@ -48,6 +54,9 @@ QAction* ConfigOption::addBoolean(const QString& text, QMenu* parent) {
 	QObject::connect(action, &QAction::triggered, [this, action]() {
 		emit valueChanged(action->isChecked());
 	});
+	QObject::connect(parent, &QAction::destroyed, [this, action]() {
+		m_actions.removeAll(qMakePair(action, 1));
+	});
 	parent->addAction(action);
 	m_actions.append(qMakePair(action, 1));
 	return action;
@@ -76,7 +85,10 @@ void ConfigOption::setValue(const QVariant& value) {
 		action.first->setChecked(value == action.second);
 		action.first->blockSignals(signalsEnabled);
 	}
-	m_slot(value);
+	std::function<void(const QVariant&)> slot;
+	foreach(slot, m_slots.values()) {
+		slot(value);
+	}
 }
 
 ConfigController::ConfigController(QObject* parent)
diff --git a/src/platform/qt/ConfigController.h b/src/platform/qt/ConfigController.h
index 1a0997057..14c83471f 100644
--- a/src/platform/qt/ConfigController.h
+++ b/src/platform/qt/ConfigController.h
@@ -32,11 +32,11 @@ Q_OBJECT
 public:
 	ConfigOption(QObject* parent = nullptr);
 
-	void connect(std::function<void(const QVariant&)>);
+	void connect(std::function<void(const QVariant&)>, QObject* parent = nullptr);
 
-	QAction* addValue(const QString& text, const QVariant& value, QMenu* parent = 0);
-	QAction* addValue(const QString& text, const char* value, QMenu* parent = 0);
-	QAction* addBoolean(const QString& text, QMenu* parent = 0);
+	QAction* addValue(const QString& text, const QVariant& value, QMenu* parent = nullptr);
+	QAction* addValue(const QString& text, const char* value, QMenu* parent = nullptr);
+	QAction* addBoolean(const QString& text, QMenu* parent = nullptr);
 
 public slots:
 	void setValue(bool value);
@@ -49,7 +49,7 @@ signals:
 	void valueChanged(const QVariant& value);
 
 private:
-	std::function<void(const QVariant&)> m_slot;
+	QMap<QObject*, std::function<void(const QVariant&)>> m_slots;
 	QList<QPair<QAction*, QVariant>> m_actions;
 };
 
diff --git a/src/platform/qt/GameController.cpp b/src/platform/qt/GameController.cpp
index 35b55085d..2c9ea7158 100644
--- a/src/platform/qt/GameController.cpp
+++ b/src/platform/qt/GameController.cpp
@@ -7,6 +7,7 @@
 
 #include "AudioProcessor.h"
 #include "InputController.h"
+#include "MultiplayerController.h"
 
 #include <QDateTime>
 #include <QThread>
@@ -41,6 +42,7 @@ GameController::GameController(QObject* parent)
 	, m_turbo(false)
 	, m_turboForced(false)
 	, m_inputController(nullptr)
+	, m_multiplayer(nullptr)
 {
 	m_renderer = new GBAVideoSoftwareRenderer;
 	GBAVideoSoftwareRendererCreate(m_renderer);
@@ -140,12 +142,30 @@ GameController::~GameController() {
 	m_audioThread->quit();
 	m_audioThread->wait();
 	disconnect();
+	clearMultiplayerController();
 	closeGame();
 	GBACheatDeviceDestroy(&m_cheatDevice);
 	delete m_renderer;
 	delete[] m_drawContext;
 }
 
+void GameController::setMultiplayerController(std::shared_ptr<MultiplayerController> controller) {
+	if (controller == m_multiplayer) {
+		return;
+	}
+	clearMultiplayerController();
+	m_multiplayer = controller;
+	controller->attachGame(this);
+}
+
+void GameController::clearMultiplayerController() {
+	if (!m_multiplayer) {
+		return;
+	}
+	m_multiplayer->detachGame(this);
+	m_multiplayer.reset();
+}
+
 void GameController::setOverride(const GBACartridgeOverride& override) {
 	m_threadContext.override = override;
 	m_threadContext.hasOverride = true;
diff --git a/src/platform/qt/GameController.h b/src/platform/qt/GameController.h
index f05337057..eb3a1580c 100644
--- a/src/platform/qt/GameController.h
+++ b/src/platform/qt/GameController.h
@@ -12,6 +12,8 @@
 #include <QMutex>
 #include <QString>
 
+#include <memory>
+
 extern "C" {
 #include "gba/cheats.h"
 #include "gba/hardware.h"
@@ -32,6 +34,7 @@ namespace QGBA {
 
 class AudioProcessor;
 class InputController;
+class MultiplayerController;
 
 class GameController : public QObject {
 Q_OBJECT
@@ -59,6 +62,10 @@ public:
 	void setInputController(InputController* controller) { m_inputController = controller; }
 	void setOverrides(Configuration* overrides) { m_threadContext.overrides = overrides; }
 
+	void setMultiplayerController(std::shared_ptr<MultiplayerController> controller);
+	std::shared_ptr<MultiplayerController> multiplayerController() { return m_multiplayer; }
+	void clearMultiplayerController();
+
 	void setOverride(const GBACartridgeOverride& override);
 	void clearOverride() { m_threadContext.hasOverride = false; }
 
@@ -167,6 +174,7 @@ private:
 	bool m_turboForced;
 
 	InputController* m_inputController;
+	std::shared_ptr<MultiplayerController> m_multiplayer;
 
 	struct GameControllerLux : GBALuminanceSource {
 		GameController* p;
diff --git a/src/platform/qt/InputController.cpp b/src/platform/qt/InputController.cpp
index 21986e48c..592761c08 100644
--- a/src/platform/qt/InputController.cpp
+++ b/src/platform/qt/InputController.cpp
@@ -19,8 +19,9 @@ extern "C" {
 
 using namespace QGBA;
 
-InputController::InputController(QObject* parent)
+InputController::InputController(int playerId, QObject* parent)
 	: QObject(parent)
+	, m_playerId(playerId)
 	, m_config(nullptr)
 	, m_gamepadTimer(nullptr)
 {
@@ -28,9 +29,8 @@ InputController::InputController(QObject* parent)
 
 #ifdef BUILD_SDL
 	m_sdlEvents.bindings = &m_inputMap;
-	GBASDLInitEvents(&m_sdlEvents);
+	GBASDLInitEvents(&m_sdlEvents, playerId);
 	GBASDLInitBindings(&m_inputMap);
-	SDL_JoystickEventState(SDL_QUERY);
 
 	m_gamepadTimer = new QTimer(this);
 	connect(m_gamepadTimer, SIGNAL(timeout()), this, SLOT(testGamepad()));
diff --git a/src/platform/qt/InputController.h b/src/platform/qt/InputController.h
index 14877e3f2..1ed729064 100644
--- a/src/platform/qt/InputController.h
+++ b/src/platform/qt/InputController.h
@@ -31,7 +31,7 @@ Q_OBJECT
 public:
 	static const uint32_t KEYBOARD = 0x51545F4B;
 
-	InputController(QObject* parent = nullptr);
+	InputController(int playerId = 0, QObject* parent = nullptr);
 	~InputController();
 
 	void setConfiguration(ConfigController* config);
@@ -67,6 +67,7 @@ private:
 
 	GBAInputMap m_inputMap;
 	ConfigController* m_config;
+	int m_playerId;
 
 #ifdef BUILD_SDL
 	GBASDLEvents m_sdlEvents;
diff --git a/src/platform/qt/MultiplayerController.cpp b/src/platform/qt/MultiplayerController.cpp
new file mode 100644
index 000000000..827900c70
--- /dev/null
+++ b/src/platform/qt/MultiplayerController.cpp
@@ -0,0 +1,71 @@
+/* Copyright (c) 2013-2015 Jeffrey Pfau
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+#include "MultiplayerController.h"
+
+#include "GameController.h"
+
+using namespace QGBA;
+
+MultiplayerController::MultiplayerController() {
+	GBASIOLockstepInit(&m_lockstep);
+}
+
+MultiplayerController::~MultiplayerController() {
+	GBASIOLockstepDeinit(&m_lockstep);
+}
+
+bool MultiplayerController::attachGame(GameController* controller) {
+	MutexLock(&m_lockstep.mutex);
+	if (m_lockstep.attached == MAX_GBAS) {
+		MutexUnlock(&m_lockstep.mutex);
+		return false;
+	}
+	GBASIOLockstepNode* node = new GBASIOLockstepNode;
+	GBASIOLockstepNodeCreate(node);
+	GBASIOLockstepAttachNode(&m_lockstep, node);
+	MutexUnlock(&m_lockstep.mutex);
+
+	controller->threadInterrupt();
+	GBAThread* thread = controller->thread();
+	if (controller->isLoaded()) {
+		GBASIOSetDriver(&thread->gba->sio, &node->d, SIO_MULTI);
+	}
+	thread->sioDrivers.multiplayer = &node->d;
+	controller->threadContinue();
+	return true;
+}
+
+void MultiplayerController::detachGame(GameController* controller) {
+	controller->threadInterrupt();
+	MutexLock(&m_lockstep.mutex);
+	GBAThread* thread = nullptr;
+	for (int i = 0; i < m_lockstep.attached; ++i) {
+		thread = controller->thread();
+		if (thread->sioDrivers.multiplayer == &m_lockstep.players[i]->d) {
+			break;
+		}
+		thread = nullptr;
+	}
+	if (thread) {
+		GBASIOLockstepNode* node = reinterpret_cast<GBASIOLockstepNode*>(thread->sioDrivers.multiplayer);
+		if (controller->isLoaded()) {
+			GBASIOSetDriver(&thread->gba->sio, nullptr, SIO_MULTI);
+		}
+		thread->sioDrivers.multiplayer = nullptr;
+		GBASIOLockstepDetachNode(&m_lockstep, node);
+		delete node;
+	}
+	MutexUnlock(&m_lockstep.mutex);
+	controller->threadContinue();
+}
+
+int MultiplayerController::attached() {
+	int num;
+	MutexLock(&m_lockstep.mutex);
+	num = m_lockstep.attached;
+	MutexUnlock(&m_lockstep.mutex);
+	return num;
+}
diff --git a/src/platform/qt/MultiplayerController.h b/src/platform/qt/MultiplayerController.h
new file mode 100644
index 000000000..ac3514c1b
--- /dev/null
+++ b/src/platform/qt/MultiplayerController.h
@@ -0,0 +1,32 @@
+/* Copyright (c) 2013-2015 Jeffrey Pfau
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+#ifndef QGBA_MULTIPLAYER_CONTROLLER
+#define QGBA_MULTIPLAYER_CONTROLLER
+
+extern "C" {
+#include "gba/sio/lockstep.h"
+}
+
+namespace QGBA {
+
+class GameController;
+
+class MultiplayerController {
+public:
+	MultiplayerController();
+	~MultiplayerController();
+
+	bool attachGame(GameController*);
+	void detachGame(GameController*);
+
+	int attached();
+
+private:
+	GBASIOLockstep m_lockstep;
+};
+
+}
+#endif
diff --git a/src/platform/qt/Window.cpp b/src/platform/qt/Window.cpp
index 89cd0cdec..0fea4b3a2 100644
--- a/src/platform/qt/Window.cpp
+++ b/src/platform/qt/Window.cpp
@@ -23,6 +23,7 @@
 #include "GIFView.h"
 #include "LoadSaveState.h"
 #include "LogView.h"
+#include "MultiplayerController.h"
 #include "OverrideView.h"
 #include "SensorView.h"
 #include "SettingsView.h"
@@ -36,13 +37,14 @@ extern "C" {
 
 using namespace QGBA;
 
-Window::Window(ConfigController* config, QWidget* parent)
+Window::Window(ConfigController* config, int playerId, QWidget* parent)
 	: QMainWindow(parent)
 	, m_logView(new LogView())
 	, m_stateWindow(nullptr)
 	, m_screenWidget(new WindowBackground())
 	, m_logo(":/res/mgba-1024.png")
 	, m_config(config)
+	, m_inputController(playerId)
 #ifdef USE_FFMPEG
 	, m_videoView(nullptr)
 #endif
@@ -54,6 +56,7 @@ Window::Window(ConfigController* config, QWidget* parent)
 #endif
 	, m_mruMenu(nullptr)
 	, m_shortcutController(new ShortcutController(this))
+	, m_playerId(playerId)
 {
 	setWindowTitle(PROJECT_NAME);
 	setFocusPolicy(Qt::StrongFocus);
@@ -525,8 +528,23 @@ void Window::setupMenu(QMenuBar* menubar) {
 		quickSaveMenu->addAction(quickSave);
 	}
 
-#ifndef Q_OS_MAC
 	fileMenu->addSeparator();
+	QAction* multiWindow = new QAction(tr("New multiplayer window"), fileMenu);
+	connect(multiWindow, &QAction::triggered, [this]() {
+		std::shared_ptr<MultiplayerController> multiplayer = m_controller->multiplayerController();
+		if (!multiplayer) {
+			multiplayer = std::make_shared<MultiplayerController>();
+			m_controller->setMultiplayerController(multiplayer);
+		}
+		Window* w2 = new Window(m_config, multiplayer->attached());
+		w2->setAttribute(Qt::WA_DeleteOnClose);
+		w2->loadConfig();
+		w2->controller()->setMultiplayerController(multiplayer);
+		w2->show();
+	});
+	addControlledAction(fileMenu, multiWindow, "multiWindow");
+
+#ifndef Q_OS_MAC
 	addControlledAction(fileMenu, fileMenu->addAction(tr("E&xit"), this, SLOT(close()), QKeySequence::Quit), "quit");
 #endif
 
@@ -585,12 +603,16 @@ void Window::setupMenu(QMenuBar* menubar) {
 
 	ConfigOption* videoSync = m_config->addOption("videoSync");
 	videoSync->addBoolean(tr("Sync to &video"), emulationMenu);
-	videoSync->connect([this](const QVariant& value) { m_controller->setVideoSync(value.toBool()); });
+	videoSync->connect([this](const QVariant& value) {
+		m_controller->setVideoSync(value.toBool());
+	}, this);
 	m_config->updateOption("videoSync");
 
 	ConfigOption* audioSync = m_config->addOption("audioSync");
 	audioSync->addBoolean(tr("Sync to &audio"), emulationMenu);
-	audioSync->connect([this](const QVariant& value) { m_controller->setAudioSync(value.toBool()); });
+	audioSync->connect([this](const QVariant& value) {
+		m_controller->setAudioSync(value.toBool());
+	}, this);
 	m_config->updateOption("audioSync");
 
 	QMenu* avMenu = menubar->addMenu(tr("Audio/&Video"));
@@ -609,17 +631,23 @@ void Window::setupMenu(QMenuBar* menubar) {
 
 	ConfigOption* lockAspectRatio = m_config->addOption("lockAspectRatio");
 	lockAspectRatio->addBoolean(tr("Lock aspect ratio"), avMenu);
-	lockAspectRatio->connect([this](const QVariant& value) { m_display->lockAspectRatio(value.toBool()); });
+	lockAspectRatio->connect([this](const QVariant& value) {
+		m_display->lockAspectRatio(value.toBool());
+	}, this);
 	m_config->updateOption("lockAspectRatio");
 
 	ConfigOption* resampleVideo = m_config->addOption("resampleVideo");
 	resampleVideo->addBoolean(tr("Resample video"), avMenu);
-	resampleVideo->connect([this](const QVariant& value) { m_display->filter(value.toBool()); });
+	resampleVideo->connect([this](const QVariant& value) {
+		m_display->filter(value.toBool());
+	}, this);
 	m_config->updateOption("resampleVideo");
 
 	QMenu* skipMenu = avMenu->addMenu(tr("Frame&skip"));
 	ConfigOption* skip = m_config->addOption("frameskip");
-	skip->connect([this](const QVariant& value) { m_controller->setFrameskip(value.toInt()); });
+	skip->connect([this](const QVariant& value) {
+		m_controller->setFrameskip(value.toInt());
+	}, this);
 	for (int i = 0; i <= 10; ++i) {
 		skip->addValue(QString::number(i), i, skipMenu);
 	}
@@ -629,7 +657,9 @@ void Window::setupMenu(QMenuBar* menubar) {
 
 	QMenu* buffersMenu = avMenu->addMenu(tr("Audio buffer &size"));
 	ConfigOption* buffers = m_config->addOption("audioBuffers");
-	buffers->connect([this](const QVariant& value) { emit audioBufferSamplesChanged(value.toInt()); });
+	buffers->connect([this](const QVariant& value) {
+		emit audioBufferSamplesChanged(value.toInt());
+	}, this);
 	buffers->addValue(tr("512"), 512, buffersMenu);
 	buffers->addValue(tr("768"), 768, buffersMenu);
 	buffers->addValue(tr("1024"), 1024, buffersMenu);
@@ -641,7 +671,9 @@ void Window::setupMenu(QMenuBar* menubar) {
 
 	QMenu* target = avMenu->addMenu("FPS target");
 	ConfigOption* fpsTargetOption = m_config->addOption("fpsTarget");
-	fpsTargetOption->connect([this](const QVariant& value) { emit fpsTargetChanged(value.toInt()); });
+	fpsTargetOption->connect([this](const QVariant& value) {
+		emit fpsTargetChanged(value.toInt());
+	}, this);
 	fpsTargetOption->addValue(tr("15"), 15, target);
 	fpsTargetOption->addValue(tr("30"), 30, target);
 	fpsTargetOption->addValue(tr("45"), 45, target);
@@ -733,19 +765,27 @@ void Window::setupMenu(QMenuBar* menubar) {
 #endif
 
 	ConfigOption* skipBios = m_config->addOption("skipBios");
-	skipBios->connect([this](const QVariant& value) { m_controller->setSkipBIOS(value.toBool()); });
+	skipBios->connect([this](const QVariant& value) {
+		m_controller->setSkipBIOS(value.toBool());
+	}, this);
 
 	ConfigOption* useBios = m_config->addOption("useBios");
 	useBios->connect([this](const QVariant& value) { m_controller->setUseBIOS(value.toBool()); });
 
 	ConfigOption* rewindEnable = m_config->addOption("rewindEnable");
-	rewindEnable->connect([this](const QVariant& value) { m_controller->setRewind(value.toBool(), m_config->getOption("rewindBufferCapacity").toInt(), m_config->getOption("rewindBufferInterval").toInt()); });
+	rewindEnable->connect([this](const QVariant& value) {
+		m_controller->setRewind(value.toBool(), m_config->getOption("rewindBufferCapacity").toInt(), m_config->getOption("rewindBufferInterval").toInt());
+	}, this);
 
 	ConfigOption* rewindBufferCapacity = m_config->addOption("rewindBufferCapacity");
-	rewindBufferCapacity->connect([this](const QVariant& value) { m_controller->setRewind(m_config->getOption("rewindEnable").toInt(), value.toInt(), m_config->getOption("rewindBufferInterval").toInt()); });
+	rewindBufferCapacity->connect([this](const QVariant& value) {
+		m_controller->setRewind(m_config->getOption("rewindEnable").toInt(), value.toInt(), m_config->getOption("rewindBufferInterval").toInt());
+	}, this);
 
 	ConfigOption* rewindBufferInterval = m_config->addOption("rewindBufferInterval");
-	rewindBufferInterval->connect([this](const QVariant& value) { m_controller->setRewind(m_config->getOption("rewindEnable").toInt(), m_config->getOption("rewindBufferCapacity").toInt(), value.toInt()); });
+	rewindBufferInterval->connect([this](const QVariant& value) {
+		m_controller->setRewind(m_config->getOption("rewindEnable").toInt(), m_config->getOption("rewindBufferCapacity").toInt(), value.toInt());
+	}, this);
 
 	QMenu* other = new QMenu(tr("Other"), this);
 	m_shortcutController->addMenu(other);
diff --git a/src/platform/qt/Window.h b/src/platform/qt/Window.h
index 68aac1697..9dce80b42 100644
--- a/src/platform/qt/Window.h
+++ b/src/platform/qt/Window.h
@@ -39,7 +39,7 @@ class Window : public QMainWindow {
 Q_OBJECT
 
 public:
-	Window(ConfigController* config, QWidget* parent = nullptr);
+	Window(ConfigController* config, int playerId = 0, QWidget* parent = nullptr);
 	virtual ~Window();
 
 	GameController* controller() { return m_controller; }
@@ -134,6 +134,7 @@ private:
 	QList<QString> m_mruFiles;
 	QMenu* m_mruMenu;
 	ShortcutController* m_shortcutController;
+	int m_playerId;
 
 #ifdef USE_FFMPEG
 	VideoView* m_videoView;
diff --git a/src/platform/sdl/main.c b/src/platform/sdl/main.c
index 71911c29b..eb7a758c6 100644
--- a/src/platform/sdl/main.c
+++ b/src/platform/sdl/main.c
@@ -105,7 +105,7 @@ int main(int argc, char** argv) {
 
 	renderer.events.bindings = &inputMap;
 	GBASDLInitBindings(&inputMap);
-	GBASDLInitEvents(&renderer.events);
+	GBASDLInitEvents(&renderer.events, 0);
 	GBASDLEventsLoadConfig(&renderer.events, GBAConfigGetInput(&config));
 	context.overrides = GBAConfigGetOverrides(&config);
 
diff --git a/src/platform/sdl/sdl-events.c b/src/platform/sdl/sdl-events.c
index e8d381b63..fb9a83e92 100644
--- a/src/platform/sdl/sdl-events.c
+++ b/src/platform/sdl/sdl-events.c
@@ -21,13 +21,13 @@
 
 static int _openContexts = 0;
 
-bool GBASDLInitEvents(struct GBASDLEvents* context) {
+bool GBASDLInitEvents(struct GBASDLEvents* context, int playerId) {
 	if (!_openContexts && SDL_InitSubSystem(SDL_INIT_JOYSTICK) < 0) {
 		return false;
 	}
 	++_openContexts;
 	SDL_JoystickEventState(SDL_ENABLE);
-	context->joystick = SDL_JoystickOpen(0);
+	context->joystick = SDL_JoystickOpen(playerId);
 #if !SDL_VERSION_ATLEAST(2, 0, 0)
 	SDL_EnableKeyRepeat(SDL_DEFAULT_REPEAT_DELAY, SDL_DEFAULT_REPEAT_INTERVAL);
 #endif
diff --git a/src/platform/sdl/sdl-events.h b/src/platform/sdl/sdl-events.h
index 997345e73..1e8e3a2a2 100644
--- a/src/platform/sdl/sdl-events.h
+++ b/src/platform/sdl/sdl-events.h
@@ -28,7 +28,7 @@ struct GBASDLEvents {
 #endif
 };
 
-bool GBASDLInitEvents(struct GBASDLEvents*);
+bool GBASDLInitEvents(struct GBASDLEvents*, int playerId);
 void GBASDLDeinitEvents(struct GBASDLEvents*);
 
 void GBASDLInitBindings(struct GBAInputMap* inputMap);