diff --git a/React/Fabric/RCTScheduler.h b/React/Fabric/RCTScheduler.h
index cee65a22e..d747032a1 100644
--- a/React/Fabric/RCTScheduler.h
+++ b/React/Fabric/RCTScheduler.h
@@ -39,17 +39,19 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (instancetype)initWithContextContainer:(std::shared_ptr<void>)contextContatiner;
 
-- (void)registerRootTag:(ReactTag)tag;
+- (void)startSurfaceWithSurfaceId:(facebook::react::SurfaceId)surfaceId
+                       moduleName:(NSString *)moduleName
+                     initailProps:(NSDictionary *)initialProps;
 
-- (void)unregisterRootTag:(ReactTag)tag;
+- (void)stopSurfaceWithSurfaceId:(facebook::react::SurfaceId)surfaceId;
 
-- (CGSize)measureWithLayoutConstraints:(facebook::react::LayoutConstraints)layoutConstraints
-                         layoutContext:(facebook::react::LayoutContext)layoutContext
-                               rootTag:(ReactTag)rootTag;
-
-- (void)constraintLayoutWithLayoutConstraints:(facebook::react::LayoutConstraints)layoutConstraints
+- (CGSize)measureSurfaceWithLayoutConstraints:(facebook::react::LayoutConstraints)layoutConstraints
                                 layoutContext:(facebook::react::LayoutContext)layoutContext
-                                      rootTag:(ReactTag)rootTag;
+                                    surfaceId:(facebook::react::SurfaceId)surfaceId;
+
+- (void)constraintSurfaceLayoutWithLayoutConstraints:(facebook::react::LayoutConstraints)layoutConstraints
+                                       layoutContext:(facebook::react::LayoutContext)layoutContext
+                                           surfaceId:(facebook::react::SurfaceId)surfaceId;
 
 @end
 
diff --git a/React/Fabric/RCTScheduler.mm b/React/Fabric/RCTScheduler.mm
index d1aa3a043..7a1822dd9 100644
--- a/React/Fabric/RCTScheduler.mm
+++ b/React/Fabric/RCTScheduler.mm
@@ -11,6 +11,8 @@
 #import <fabric/uimanager/Scheduler.h>
 #import <fabric/uimanager/SchedulerDelegate.h>
 
+#import <React/RCTFollyConvert.h>
+
 #import "RCTConversions.h"
 
 using namespace facebook::react;
@@ -55,28 +57,34 @@ private:
   _scheduler->setDelegate(nullptr);
 }
 
-- (void)registerRootTag:(ReactTag)tag
+- (void)startSurfaceWithSurfaceId:(SurfaceId)surfaceId
+                       moduleName:(NSString *)moduleName
+                     initailProps:(NSDictionary *)initialProps
 {
-  _scheduler->registerRootTag(tag);
+  _scheduler->startSurface(
+    surfaceId,
+    RCTStringFromNSString(moduleName),
+    convertIdToFollyDynamic(initialProps)
+  );
 }
 
-- (void)unregisterRootTag:(ReactTag)tag
+- (void)stopSurfaceWithSurfaceId:(SurfaceId)surfaceId
 {
-  _scheduler->unregisterRootTag(tag);
+  _scheduler->stopSurface(surfaceId);
 }
 
-- (CGSize)measureWithLayoutConstraints:(LayoutConstraints)layoutConstraints
-                         layoutContext:(LayoutContext)layoutContext
-                               rootTag:(ReactTag)rootTag
-{
-  return RCTCGSizeFromSize(_scheduler->measure(rootTag, layoutConstraints, layoutContext));
-}
-
-- (void)constraintLayoutWithLayoutConstraints:(LayoutConstraints)layoutConstraints
+- (CGSize)measureSurfaceWithLayoutConstraints:(LayoutConstraints)layoutConstraints
                                 layoutContext:(LayoutContext)layoutContext
-                                      rootTag:(ReactTag)rootTag
+                                    surfaceId:(SurfaceId)surfaceId
 {
-  _scheduler->constraintLayout(rootTag, layoutConstraints, layoutContext);
+  return RCTCGSizeFromSize(_scheduler->measureSurface(surfaceId, layoutConstraints, layoutContext));
+}
+
+- (void)constraintSurfaceLayoutWithLayoutConstraints:(LayoutConstraints)layoutConstraints
+                                       layoutContext:(LayoutContext)layoutContext
+                                           surfaceId:(SurfaceId)surfaceId
+{
+  _scheduler->constraintSurfaceLayout(surfaceId, layoutConstraints, layoutContext);
 }
 
 @end
diff --git a/React/Fabric/RCTSurfacePresenter.mm b/React/Fabric/RCTSurfacePresenter.mm
index 977cfbbae..d6514f2c9 100644
--- a/React/Fabric/RCTSurfacePresenter.mm
+++ b/React/Fabric/RCTSurfacePresenter.mm
@@ -150,9 +150,9 @@ using namespace facebook::react;
   layoutConstraints.minimumSize = RCTSizeFromCGSize(minimumSize);
   layoutConstraints.maximumSize = RCTSizeFromCGSize(maximumSize);
 
-  return [_scheduler measureWithLayoutConstraints:layoutConstraints
-                                    layoutContext:layoutContext
-                                          rootTag:surface.rootTag];
+  return [_scheduler measureSurfaceWithLayoutConstraints:layoutConstraints
+                                           layoutContext:layoutContext
+                                               surfaceId:surface.rootTag];
 }
 
 - (void)setMinimumSize:(CGSize)minimumSize
@@ -167,9 +167,9 @@ using namespace facebook::react;
   layoutConstraints.minimumSize = RCTSizeFromCGSize(minimumSize);
   layoutConstraints.maximumSize = RCTSizeFromCGSize(maximumSize);
 
-  [_scheduler constraintLayoutWithLayoutConstraints:layoutConstraints
-                                      layoutContext:layoutContext
-                                            rootTag:surface.rootTag];
+  [_scheduler constraintSurfaceLayoutWithLayoutConstraints:layoutConstraints
+                                             layoutContext:layoutContext
+                                                 surfaceId:surface.rootTag];
 }
 
 - (void)startSurface:(RCTFabricSurface *)surface
@@ -177,27 +177,21 @@ using namespace facebook::react;
   [_mountingManager.componentViewRegistry dequeueComponentViewWithName:@"Root" tag:surface.rootTag];
 
   [self createSchedulerIfNeeded];
-  [_scheduler registerRootTag:surface.rootTag];
+
+  [_scheduler startSurfaceWithSurfaceId:surface.rootTag
+                             moduleName:surface.moduleName
+                           initailProps:surface.properties];
 
   [self setMinimumSize:surface.minimumSize
            maximumSize:surface.maximumSize
                surface:surface];
-
-  // TODO: Move this down to Scheduler.
-  NSDictionary *applicationParameters = @{
-    @"rootTag": @(surface.rootTag),
-    @"initialProps": surface.properties,
-  };
-  [self->_batchedBridge enqueueJSCall:@"AppRegistry" method:@"runApplication" args:@[surface.moduleName, applicationParameters] completion:NULL];
 }
 
 - (void)stopSurface:(RCTFabricSurface *)surface
 {
-  // TODO: Move this down to Scheduler.
-  [_batchedBridge enqueueJSCall:@"ReactFabric" method:@"unmountComponentAtNode" args:@[@(surface.rootTag)] completion:NULL];
-
   [self ensureSchedulerDoesExist];
-  [_scheduler unregisterRootTag:surface.rootTag];
+
+  [_scheduler stopSurfaceWithSurfaceId:surface.rootTag];
 
   UIView<RCTComponentViewProtocol> *rootView = [_mountingManager.componentViewRegistry componentViewByTag:surface.rootTag];
   [_mountingManager.componentViewRegistry enqueueComponentViewWithName:@"Root" tag:surface.rootTag componentView:rootView];
diff --git a/ReactCommon/fabric/core/primitives/ReactPrimitives.h b/ReactCommon/fabric/core/primitives/ReactPrimitives.h
index a68719f72..72ecba50c 100644
--- a/ReactCommon/fabric/core/primitives/ReactPrimitives.h
+++ b/ReactCommon/fabric/core/primitives/ReactPrimitives.h
@@ -22,6 +22,11 @@ namespace react {
 using Tag = int32_t;
 using InstanceHandle = struct InstanceHandleDummyStruct {} *;
 
+/*
+ * An id of a running Surface instance that is used to refer to the instance.
+ */
+using SurfaceId = int32_t;
+
 /*
  * `RawProps` represents untyped map with props comes from JavaScript side.
  */
diff --git a/ReactCommon/fabric/uimanager/FabricUIManager.cpp b/ReactCommon/fabric/uimanager/FabricUIManager.cpp
index 0101bed13..e3e71ac53 100644
--- a/ReactCommon/fabric/uimanager/FabricUIManager.cpp
+++ b/ReactCommon/fabric/uimanager/FabricUIManager.cpp
@@ -106,7 +106,7 @@ static const std::string componentNameByReactViewName(std::string viewName) {
 FabricUIManager::~FabricUIManager() {
   (*executor_)([this] {
     uninstaller_();
-  }, EventBeatBasedExecutor::Mode::Synchronous);
+  });
 }
 
 void FabricUIManager::setComponentDescriptorRegistry(const SharedComponentDescriptorRegistry &componentDescriptorRegistry) {
@@ -129,6 +129,14 @@ void FabricUIManager::setDispatchEventToTargetFunction(std::function<DispatchEve
   dispatchEventToTargetFunction_ = dispatchEventFunction;
 }
 
+void FabricUIManager::setStartSurfaceFunction(std::function<StartSurface> startSurfaceFunction) {
+  startSurfaceFunction_ = startSurfaceFunction;
+}
+
+void FabricUIManager::setStopSurfaceFunction(std::function<StopSurface> stopSurfaceFunction) {
+  stopSurfaceFunction_ = stopSurfaceFunction;
+}
+
 void FabricUIManager::dispatchEventToTarget(const EventTarget *eventTarget, const std::string &type, const folly::dynamic &payload) const {
   if (eventTarget) {
     dispatchEventToTargetFunction_(
@@ -146,6 +154,18 @@ void FabricUIManager::dispatchEventToTarget(const EventTarget *eventTarget, cons
   }
 }
 
+void FabricUIManager::startSurface(SurfaceId surfaceId, const std::string &moduleName, const folly::dynamic &initialProps) const {
+  (*executor_)([this, surfaceId, moduleName, initialProps] {
+    startSurfaceFunction_(surfaceId, moduleName, initialProps);
+  });
+}
+
+void FabricUIManager::stopSurface(SurfaceId surfaceId) const {
+  (*executor_)([this, surfaceId] {
+    stopSurfaceFunction_(surfaceId);
+  });
+}
+
 SharedShadowNode FabricUIManager::createNode(int tag, std::string viewName, int rootTag, folly::dynamic props, SharedEventTarget eventTarget) const {
   isLoggingEnabled && LOG(INFO) << "FabricUIManager::createNode(tag: " << tag << ", name: " << viewName << ", rootTag: " << rootTag << ", props: " << props << ")";
 
diff --git a/ReactCommon/fabric/uimanager/FabricUIManager.h b/ReactCommon/fabric/uimanager/FabricUIManager.h
index 70ae48291..3481faecc 100644
--- a/ReactCommon/fabric/uimanager/FabricUIManager.h
+++ b/ReactCommon/fabric/uimanager/FabricUIManager.h
@@ -32,6 +32,9 @@ using UIManagerUninstaller = void ();
 using DispatchEventToEmptyTargetFunction = void (const EventHandler &eventHandler, const std::string &type, const folly::dynamic &payload);
 using DispatchEventToTargetFunction = void (const EventHandler &eventHandler, const EventTarget &eventTarget, const std::string &type, const folly::dynamic &payload);
 
+using StartSurface = void (SurfaceId surfaceId, const std::string &moduleName, const folly::dynamic &initalProps);
+using StopSurface = void (SurfaceId surfaceId);
+
 class FabricUIManager {
 public:
 
@@ -61,10 +64,14 @@ public:
    */
   void setDispatchEventToEmptyTargetFunction(std::function<DispatchEventToEmptyTargetFunction> dispatchEventFunction);
   void setDispatchEventToTargetFunction(std::function<DispatchEventToTargetFunction> dispatchEventFunction);
+  void setStartSurfaceFunction(std::function<StartSurface>);
+  void setStopSurfaceFunction(std::function<StopSurface>);
 
 #pragma mark - Native-facing Interface
 
   void dispatchEventToTarget(const EventTarget *eventTarget, const std::string &type, const folly::dynamic &payload) const;
+  void startSurface(SurfaceId surfaceId, const std::string &moduleName, const folly::dynamic &initialProps) const;
+  void stopSurface(SurfaceId surfaceId) const;
 
 #pragma mark - JavaScript/React-facing Interface
 
@@ -86,12 +93,13 @@ public:
   void registerEventHandler(UniqueEventHandler eventHandler) const;
 
 private:
-
   SharedComponentDescriptorRegistry componentDescriptorRegistry_;
   UIManagerDelegate *delegate_;
   mutable UniqueEventHandler eventHandler_;
   std::function<DispatchEventToEmptyTargetFunction> dispatchEventToEmptyTargetFunction_;
   std::function<DispatchEventToTargetFunction> dispatchEventToTargetFunction_;
+  std::function<StartSurface> startSurfaceFunction_;
+  std::function<StopSurface> stopSurfaceFunction_;
 
   std::unique_ptr<EventBeatBasedExecutor> executor_;
   std::function<UIManagerInstaller> installer_;
diff --git a/ReactCommon/fabric/uimanager/Scheduler.cpp b/ReactCommon/fabric/uimanager/Scheduler.cpp
index aeb92eda0..6f73f6314 100644
--- a/ReactCommon/fabric/uimanager/Scheduler.cpp
+++ b/ReactCommon/fabric/uimanager/Scheduler.cpp
@@ -51,14 +51,30 @@ Scheduler::~Scheduler() {
   uiManager_->setDelegate(nullptr);
 }
 
-void Scheduler::registerRootTag(Tag rootTag) {
-  auto shadowTree = std::make_unique<ShadowTree>(rootTag);
+void Scheduler::startSurface(
+  SurfaceId surfaceId,
+  const std::string &moduleName,
+  const folly::dynamic &initialProps
+) const {
+  std::lock_guard<std::mutex> lock(mutex_);
+
+  auto shadowTree = std::make_unique<ShadowTree>(surfaceId);
   shadowTree->setDelegate(this);
-  shadowTreeRegistry_.emplace(rootTag, std::move(shadowTree));
+  shadowTreeRegistry_.emplace(surfaceId, std::move(shadowTree));
+
+#ifndef ANDROID
+  uiManager_->startSurface(surfaceId, moduleName, initialProps);
+#endif
 }
 
-void Scheduler::unregisterRootTag(Tag rootTag) {
-  const auto &iterator = shadowTreeRegistry_.find(rootTag);
+void Scheduler::stopSurface(SurfaceId surfaceId) const {
+  std::lock_guard<std::mutex> lock(mutex_);
+
+#ifndef ANDROID
+  uiManager_->stopSurface(surfaceId);
+#endif
+
+  const auto &iterator = shadowTreeRegistry_.find(surfaceId);
   const auto &shadowTree = iterator->second;
   assert(shadowTree);
   // As part of stopping the Surface, we have to commit an empty tree.
@@ -67,14 +83,24 @@ void Scheduler::unregisterRootTag(Tag rootTag) {
   shadowTreeRegistry_.erase(iterator);
 }
 
-Size Scheduler::measure(const Tag &rootTag, const LayoutConstraints &layoutConstraints, const LayoutContext &layoutContext) const {
-  const auto &shadowTree = shadowTreeRegistry_.at(rootTag);
+Size Scheduler::measureSurface(
+  SurfaceId surfaceId,
+  const LayoutConstraints &layoutConstraints,
+  const LayoutContext &layoutContext
+) const {
+  std::lock_guard<std::mutex> lock(mutex_);
+  const auto &shadowTree = shadowTreeRegistry_.at(surfaceId);
   assert(shadowTree);
   return shadowTree->measure(layoutConstraints, layoutContext);
 }
 
-void Scheduler::constraintLayout(const Tag &rootTag, const LayoutConstraints &layoutConstraints, const LayoutContext &layoutContext) {
-  const auto &shadowTree = shadowTreeRegistry_.at(rootTag);
+void Scheduler::constraintSurfaceLayout(
+  SurfaceId surfaceId,
+  const LayoutConstraints &layoutConstraints,
+  const LayoutContext &layoutContext
+) const {
+  std::lock_guard<std::mutex> lock(mutex_);
+  const auto &shadowTree = shadowTreeRegistry_.at(surfaceId);
   assert(shadowTree);
   return shadowTree->constraintLayout(layoutConstraints, layoutContext);
 }
@@ -91,7 +117,7 @@ SchedulerDelegate *Scheduler::getDelegate() const {
 
 #pragma mark - ShadowTreeDelegate
 
-void Scheduler::shadowTreeDidCommit(const ShadowTree &shadowTree, const ShadowViewMutationList &mutations) {
+void Scheduler::shadowTreeDidCommit(const ShadowTree &shadowTree, const ShadowViewMutationList &mutations) const {
   if (delegate_) {
     delegate_->schedulerDidFinishTransaction(shadowTree.getRootTag(), mutations);
   }
@@ -100,6 +126,8 @@ void Scheduler::shadowTreeDidCommit(const ShadowTree &shadowTree, const ShadowVi
 #pragma mark - UIManagerDelegate
 
 void Scheduler::uiManagerDidFinishTransaction(Tag rootTag, const SharedShadowNodeUnsharedList &rootChildNodes) {
+  std::lock_guard<std::mutex> lock(mutex_);
+
   const auto iterator = shadowTreeRegistry_.find(rootTag);
   if (iterator == shadowTreeRegistry_.end()) {
     // This might happen during surface unmounting/deallocation process
diff --git a/ReactCommon/fabric/uimanager/Scheduler.h b/ReactCommon/fabric/uimanager/Scheduler.h
index aef442d48..87382a195 100644
--- a/ReactCommon/fabric/uimanager/Scheduler.h
+++ b/ReactCommon/fabric/uimanager/Scheduler.h
@@ -6,6 +6,7 @@
 #pragma once
 
 #include <memory>
+#include <mutex>
 
 #include <fabric/core/ComponentDescriptor.h>
 #include <fabric/core/LayoutConstraints.h>
@@ -28,17 +29,30 @@ class Scheduler final:
   public ShadowTreeDelegate {
 
 public:
-
   Scheduler(const SharedContextContainer &contextContainer);
   ~Scheduler();
 
-#pragma mark - Shadow Tree Management
+#pragma mark - Surface Management
 
-  void registerRootTag(Tag rootTag);
-  void unregisterRootTag(Tag rootTag);
+  void startSurface(
+    SurfaceId surfaceId,
+    const std::string &moduleName,
+    const folly::dynamic &initialProps
+  ) const;
 
-  Size measure(const Tag &rootTag, const LayoutConstraints &layoutConstraints, const LayoutContext &layoutContext) const;
-  void constraintLayout(const Tag &rootTag, const LayoutConstraints &layoutConstraints, const LayoutContext &layoutContext);
+  void stopSurface(SurfaceId surfaceId) const;
+
+  Size measureSurface(
+    SurfaceId surfaceId,
+    const LayoutConstraints &layoutConstraints,
+    const LayoutContext &layoutContext
+  ) const;
+
+  void constraintSurfaceLayout(
+    SurfaceId surfaceId,
+    const LayoutConstraints &layoutConstraints,
+    const LayoutContext &layoutContext
+  ) const;
 
 #pragma mark - Delegate
 
@@ -57,7 +71,7 @@ public:
 
 #pragma mark - ShadowTreeDelegate
 
-  void shadowTreeDidCommit(const ShadowTree &shadowTree, const ShadowViewMutationList &mutations) override;
+  void shadowTreeDidCommit(const ShadowTree &shadowTree, const ShadowViewMutationList &mutations) const override;
 
 #pragma mark - Deprecated
 
@@ -69,7 +83,8 @@ public:
 private:
   SchedulerDelegate *delegate_;
   std::shared_ptr<FabricUIManager> uiManager_;
-  std::unordered_map<Tag, std::unique_ptr<ShadowTree>> shadowTreeRegistry_;
+  mutable std::mutex mutex_;
+  mutable std::unordered_map<SurfaceId, std::unique_ptr<ShadowTree>> shadowTreeRegistry_; // Protected by `mutex_`.
   SharedEventDispatcher eventDispatcher_;
   SharedContextContainer contextContainer_;
 };
diff --git a/ReactCommon/fabric/uimanager/ShadowTree.cpp b/ReactCommon/fabric/uimanager/ShadowTree.cpp
index 4693e70f1..dd8c1e16e 100644
--- a/ReactCommon/fabric/uimanager/ShadowTree.cpp
+++ b/ReactCommon/fabric/uimanager/ShadowTree.cpp
@@ -165,11 +165,11 @@ void ShadowTree::toggleEventEmitters(const ShadowViewMutationList &mutations) {
 
 #pragma mark - Delegate
 
-void ShadowTree::setDelegate(ShadowTreeDelegate *delegate) {
+void ShadowTree::setDelegate(ShadowTreeDelegate const *delegate) {
   delegate_ = delegate;
 }
 
-ShadowTreeDelegate *ShadowTree::getDelegate() const {
+ShadowTreeDelegate const *ShadowTree::getDelegate() const {
   return delegate_;
 }
 
diff --git a/ReactCommon/fabric/uimanager/ShadowTree.h b/ReactCommon/fabric/uimanager/ShadowTree.h
index 2f7e94049..d7add5ccf 100644
--- a/ReactCommon/fabric/uimanager/ShadowTree.h
+++ b/ReactCommon/fabric/uimanager/ShadowTree.h
@@ -68,8 +68,8 @@ public:
    * The delegate is stored as a raw pointer, so the owner must null
    * the pointer before being destroyed.
    */
-  void setDelegate(ShadowTreeDelegate *delegate);
-  ShadowTreeDelegate *getDelegate() const;
+  void setDelegate(ShadowTreeDelegate const *delegate);
+  ShadowTreeDelegate const *getDelegate() const;
 
 private:
 
@@ -85,7 +85,7 @@ private:
 
   const Tag rootTag_;
   SharedRootShadowNode rootShadowNode_;
-  ShadowTreeDelegate *delegate_;
+  ShadowTreeDelegate const *delegate_;
   mutable std::mutex commitMutex_;
 };
 
diff --git a/ReactCommon/fabric/uimanager/ShadowTreeDelegate.h b/ReactCommon/fabric/uimanager/ShadowTreeDelegate.h
index 71bc3caf9..8d0f7ddea 100644
--- a/ReactCommon/fabric/uimanager/ShadowTreeDelegate.h
+++ b/ReactCommon/fabric/uimanager/ShadowTreeDelegate.h
@@ -21,7 +21,7 @@ public:
   /*
    * Called right after Shadow Tree commit a new state of the the tree.
    */
-  virtual void shadowTreeDidCommit(const ShadowTree &shadowTree, const ShadowViewMutationList &mutations) = 0;
+  virtual void shadowTreeDidCommit(const ShadowTree &shadowTree, const ShadowViewMutationList &mutations) const = 0;
 
   virtual ~ShadowTreeDelegate() noexcept = default;
 };