diff --git a/include/weave/device.h b/include/weave/device.h
index ca04bdf..2d7aaff 100644
--- a/include/weave/device.h
+++ b/include/weave/device.h
@@ -8,6 +8,7 @@
 #include <memory>
 #include <set>
 #include <string>
+#include <vector>
 
 #include <weave/command.h>
 #include <weave/export.h>
@@ -45,10 +46,74 @@
   virtual void AddSettingsChangedCallback(
       const SettingsChangedCallback& callback) = 0;
 
+  // Adds new trait definitions to device.
+  virtual void AddTraitDefinitionsFromJson(const std::string& json) = 0;
+  virtual void AddTraitDefinitions(const base::DictionaryValue& dict) = 0;
+
+  // Returns the full JSON dictionary containing trait definitions.
+  virtual const base::DictionaryValue& GetTraits() const = 0;
+
+  // Adds a new component instance to device. Traits used by this component
+  // must be already defined.
+  virtual bool AddComponent(const std::string& name,
+                            const std::vector<std::string>& traits,
+                            ErrorPtr* error) = 0;
+
+  // Sets callback which is called when new components are added.
+  virtual void AddComponentTreeChangedCallback(
+      const base::Closure& callback) = 0;
+
+  // Returns the full JSON dictionary containing component instances.
+  virtual const base::DictionaryValue& GetComponents() const = 0;
+
+  // Sets value of multiple properties of the state.
+  // It's recommended to call this to initialize component state defined.
+  // Example:
+  //   device->SetStatePropertiesFromJson("myComponent",
+  //                                      "{'base':{'firmwareVersion':'123'}}")
+  // Method completely replaces properties included |json| or |dict|.
+  // Properties of the state not included |json| or |dict| will stay unchanged.
+  virtual bool SetStatePropertiesFromJson(
+      const std::string& component,
+      const std::string& json,
+      ErrorPtr* error) = 0;
+  virtual bool SetStateProperties(
+      const std::string& component,
+      const base::DictionaryValue& dict,
+      ErrorPtr* error) = 0;
+
+  // Returns value of the single property.
+  // |name| is full property name, including trait name. e.g. "base.network".
+  virtual const base::Value* GetStateProperty(
+      const std::string& component,
+      const std::string& name,
+      ErrorPtr* error) const = 0;
+
+  // Sets value of the single property.
+  // |name| is full property name, including trait name. e.g. "base.network".
+  virtual bool SetStateProperty(
+      const std::string& component,
+      const std::string& name,
+      const base::Value& value,
+      ErrorPtr* error) = 0;
+
   // Callback type for AddCommandHandler.
   using CommandHandlerCallback =
       base::Callback<void(const std::weak_ptr<Command>& command)>;
 
+  // Sets handler for new commands added to the queue.
+  // |component| is the name of the component for which commands should be
+  // handled.
+  // |command_name| is the full command name of the command to handle. e.g.
+  // "base.reboot". Each command can have no more than one handler.
+  // Empty |component| and |command_name| sets default handler for all unhanded
+  // commands.
+  // No new command handlers can be set after default handler was set.
+  virtual void AddCommandHandler(
+      const std::string& component,
+      const std::string& command_name,
+      const CommandHandlerCallback& callback) = 0;
+
   // Adds a new command to the command queue.
   virtual bool AddCommand(const base::DictionaryValue& command,
                           std::string* id,
diff --git a/include/weave/test/mock_device.h b/include/weave/test/mock_device.h
index e5063e7..88cc5e0 100644
--- a/include/weave/test/mock_device.h
+++ b/include/weave/test/mock_device.h
@@ -21,14 +21,51 @@
   MOCK_CONST_METHOD0(GetSettings, const Settings&());
   MOCK_METHOD1(AddSettingsChangedCallback,
                void(const SettingsChangedCallback& callback));
-  MOCK_METHOD1(AddCommandDefinitionsFromJson, void(const std::string&));
-  MOCK_METHOD1(AddCommandDefinitions, void(const base::DictionaryValue&));
-  MOCK_METHOD2(AddCommandHandler,
-               void(const std::string&, const CommandHandlerCallback&));
+  MOCK_METHOD1(AddTraitDefinitionsFromJson, void(const std::string& json));
+  MOCK_METHOD1(AddTraitDefinitions, void(const base::DictionaryValue& dict));
+  MOCK_CONST_METHOD0(GetTraits, const base::DictionaryValue&());
+  MOCK_METHOD3(AddComponent, bool(const std::string& name,
+                                  const std::vector<std::string>& traits,
+                                  ErrorPtr* error));
+  MOCK_METHOD1(AddComponentTreeChangedCallback,
+               void(const base::Closure& callback));
+  MOCK_CONST_METHOD0(GetComponents, const base::DictionaryValue&());
+  MOCK_METHOD3(SetStatePropertiesFromJson, bool(const std::string& component,
+                                                const std::string& json,
+                                                ErrorPtr* error));
+  MOCK_METHOD3(SetStateProperties, bool(const std::string& component,
+                                        const base::DictionaryValue& dict,
+                                        ErrorPtr* error));
+  MOCK_CONST_METHOD3(GetStateProperty,
+                     const base::Value*(const std::string& component,
+                                        const std::string& name,
+                                        ErrorPtr* error));
+  MOCK_METHOD4(SetStateProperty, bool(const std::string& component,
+                                      const std::string& name,
+                                      const base::Value& value,
+                                      ErrorPtr* error));
+  MOCK_METHOD3(AddCommandHandler, void(const std::string& component,
+                                       const std::string& command_name,
+                                       const CommandHandlerCallback& callback));
   MOCK_METHOD3(AddCommand,
                bool(const base::DictionaryValue&, std::string*, ErrorPtr*));
   MOCK_METHOD1(FindCommand, Command*(const std::string&));
   MOCK_METHOD1(AddStateChangedCallback, void(const base::Closure& callback));
+  MOCK_CONST_METHOD0(GetGcdState, GcdState());
+  MOCK_METHOD1(AddGcdStateChangedCallback,
+               void(const GcdStateChangedCallback& callback));
+  MOCK_METHOD2(Register,
+               void(const std::string& ticket_id,
+                    const DoneCallback& callback));
+  MOCK_METHOD2(AddPairingChangedCallbacks,
+               void(const PairingBeginCallback& begin_callback,
+                    const PairingEndCallback& end_callback));
+
+  // Deprecated methods.
+  MOCK_METHOD1(AddCommandDefinitionsFromJson, void(const std::string&));
+  MOCK_METHOD1(AddCommandDefinitions, void(const base::DictionaryValue&));
+  MOCK_METHOD2(AddCommandHandler,
+               void(const std::string&, const CommandHandlerCallback&));
   MOCK_METHOD1(AddStateDefinitionsFromJson, void(const std::string&));
   MOCK_METHOD1(AddStateDefinitions, void(const base::DictionaryValue&));
   MOCK_METHOD2(SetStatePropertiesFromJson, bool(const std::string&, ErrorPtr*));
@@ -41,15 +78,6 @@
                     const base::Value& value,
                     ErrorPtr* error));
   MOCK_CONST_METHOD0(GetState, const base::DictionaryValue&());
-  MOCK_CONST_METHOD0(GetGcdState, GcdState());
-  MOCK_METHOD1(AddGcdStateChangedCallback,
-               void(const GcdStateChangedCallback& callback));
-  MOCK_METHOD2(Register,
-               void(const std::string& ticket_id,
-                    const DoneCallback& callback));
-  MOCK_METHOD2(AddPairingChangedCallbacks,
-               void(const PairingBeginCallback& begin_callback,
-                    const PairingEndCallback& end_callback));
 };
 
 }  // namespace test
diff --git a/src/device_manager.cc b/src/device_manager.cc
index 52b2882..64a8093 100644
--- a/src/device_manager.cc
+++ b/src/device_manager.cc
@@ -10,6 +10,7 @@
 
 #include "src/base_api_handler.h"
 #include "src/commands/command_manager.h"
+#include "src/component_manager.h"
 #include "src/config.h"
 #include "src/device_registration_info.h"
 #include "src/privet/privet_manager.h"
@@ -33,6 +34,7 @@
                              provider::HttpServer* http_server,
                              provider::Wifi* wifi,
                              provider::Bluetooth* bluetooth) {
+  component_manager_.reset(new ComponentManager);
   command_manager_ = std::make_shared<CommandManager>();
   state_change_queue_.reset(new StateChangeQueue(kMaxStateChangeQueueSize));
   state_manager_ = std::make_shared<StateManager>(state_change_queue_.get());
@@ -89,6 +91,65 @@
   device_info_->AddGcdStateChangedCallback(callback);
 }
 
+void DeviceManager::AddTraitDefinitionsFromJson(const std::string& json) {
+  CHECK(component_manager_->LoadTraits(json, nullptr));
+}
+
+void DeviceManager::AddTraitDefinitions(const base::DictionaryValue& dict) {
+  CHECK(component_manager_->LoadTraits(dict, nullptr));
+}
+
+const base::DictionaryValue& DeviceManager::GetTraits() const {
+  return component_manager_->GetTraits();
+}
+
+bool DeviceManager::AddComponent(const std::string& name,
+                                 const std::vector<std::string>& traits,
+                                 ErrorPtr* error) {
+  return component_manager_->AddComponent("", name, traits, error);
+}
+
+void DeviceManager::AddComponentTreeChangedCallback(
+    const base::Closure& callback) {
+  component_manager_->AddComponentTreeChangedCallback(callback);
+}
+
+const base::DictionaryValue& DeviceManager::GetComponents() const {
+  return component_manager_->GetComponents();
+}
+
+bool DeviceManager::SetStatePropertiesFromJson(const std::string& component,
+                                               const std::string& json,
+                                               ErrorPtr* error) {
+  return component_manager_->SetStatePropertiesFromJson(component, json, error);
+}
+
+bool DeviceManager::SetStateProperties(const std::string& component,
+                                       const base::DictionaryValue& dict,
+                                       ErrorPtr* error) {
+  return component_manager_->SetStateProperties(component, dict, error);
+}
+
+const base::Value* DeviceManager::GetStateProperty(
+    const std::string& component,
+    const std::string& name,
+    ErrorPtr* error) const {
+  return component_manager_->GetStateProperty(component, name, error);
+}
+
+bool DeviceManager::SetStateProperty(const std::string& component,
+                                     const std::string& name,
+                                     const base::Value& value,
+                                     ErrorPtr* error) {
+  return component_manager_->SetStateProperty(component, name, value, error);
+}
+
+void DeviceManager::AddCommandHandler(const std::string& component,
+                                      const std::string& command_name,
+                                      const CommandHandlerCallback& callback) {
+  component_manager_->AddCommandHandler(component, command_name, callback);
+}
+
 void DeviceManager::AddCommandDefinitionsFromJson(const std::string& json) {
   CHECK(command_manager_->LoadCommands(json, nullptr));
 }
diff --git a/src/device_manager.h b/src/device_manager.h
index 6c3df05..2a23755 100644
--- a/src/device_manager.h
+++ b/src/device_manager.h
@@ -13,6 +13,7 @@
 class BaseApiHandler;
 class Config;
 class CommandManager;
+class ComponentManager;
 class DeviceRegistrationInfo;
 class StateChangeQueue;
 class StateManager;
@@ -37,15 +38,48 @@
   const Settings& GetSettings() const override;
   void AddSettingsChangedCallback(
       const SettingsChangedCallback& callback) override;
-  void AddCommandDefinitionsFromJson(const std::string& json) override;
-  void AddCommandDefinitions(const base::DictionaryValue& dict) override;
+  void AddTraitDefinitionsFromJson(const std::string& json) override;
+  void AddTraitDefinitions(const base::DictionaryValue& dict) override;
+  const base::DictionaryValue& GetTraits() const override;
+  bool AddComponent(const std::string& name,
+                    const std::vector<std::string>& traits,
+                    ErrorPtr* error) override;
+  void AddComponentTreeChangedCallback(const base::Closure& callback) override;
+  const base::DictionaryValue& GetComponents() const override;
+  bool SetStatePropertiesFromJson(const std::string& component,
+                                  const std::string& json,
+                                  ErrorPtr* error) override;
+  bool SetStateProperties(const std::string& component,
+                          const base::DictionaryValue& dict,
+                          ErrorPtr* error) override;
+  const base::Value* GetStateProperty(const std::string& component,
+                                      const std::string& name,
+                                      ErrorPtr* error) const override;
+  bool SetStateProperty(const std::string& component,
+                        const std::string& name,
+                        const base::Value& value,
+                        ErrorPtr* error) override;
+  void AddCommandHandler(const std::string& component,
+                         const std::string& command_name,
+                         const CommandHandlerCallback& callback) override;
   bool AddCommand(const base::DictionaryValue& command,
                   std::string* id,
                   ErrorPtr* error) override;
   Command* FindCommand(const std::string& id) override;
+  void AddStateChangedCallback(const base::Closure& callback) override;
+  void Register(const std::string& ticket_id,
+                const DoneCallback& callback) override;
+  GcdState GetGcdState() const override;
+  void AddGcdStateChangedCallback(
+      const GcdStateChangedCallback& callback) override;
+  void AddPairingChangedCallbacks(
+      const PairingBeginCallback& begin_callback,
+      const PairingEndCallback& end_callback) override;
+
+  void AddCommandDefinitionsFromJson(const std::string& json) override;
+  void AddCommandDefinitions(const base::DictionaryValue& dict) override;
   void AddCommandHandler(const std::string& command_name,
                          const CommandHandlerCallback& callback) override;
-  void AddStateChangedCallback(const base::Closure& callback) override;
   void AddStateDefinitionsFromJson(const std::string& json) override;
   void AddStateDefinitions(const base::DictionaryValue& dict) override;
   bool SetStatePropertiesFromJson(const std::string& json,
@@ -57,14 +91,6 @@
                         const base::Value& value,
                         ErrorPtr* error) override;
   const base::DictionaryValue& GetState() const override;
-  void Register(const std::string& ticket_id,
-                const DoneCallback& callback) override;
-  GcdState GetGcdState() const override;
-  void AddGcdStateChangedCallback(
-      const GcdStateChangedCallback& callback) override;
-  void AddPairingChangedCallbacks(
-      const PairingBeginCallback& begin_callback,
-      const PairingEndCallback& end_callback) override;
 
   Config* GetConfig();
 
@@ -76,6 +102,7 @@
                    provider::Wifi* wifi,
                    provider::Bluetooth* bluetooth);
 
+  std::unique_ptr<ComponentManager> component_manager_;
   std::shared_ptr<CommandManager> command_manager_;
   std::unique_ptr<StateChangeQueue> state_change_queue_;
   std::shared_ptr<StateManager> state_manager_;