diff --git a/src/main/scala/plugin/PluginSystem.scala b/src/main/scala/plugin/PluginSystem.scala
index 18c81f5..52f5d0c 100644
--- a/src/main/scala/plugin/PluginSystem.scala
+++ b/src/main/scala/plugin/PluginSystem.scala
@@ -14,71 +14,90 @@
 
   private val logger = LoggerFactory.getLogger(PluginSystem.getClass)
 
-  private val repositoryMenuList   = ListBuffer[RepositoryMenu]()
-  private val globalMenuList       = ListBuffer[GlobalMenu]()
-  private val repositoryActionList = ListBuffer[Action]()
-  private val globalActionList     = ListBuffer[Action]()
+  private val plugins = scala.collection.mutable.Map[String, Plugin]()
 
+  def install(id: String, plugin: Plugin): Unit = {
+    plugins.put(id, plugin)
+  }
+
+  def uninstall(id: String): Unit = {
+    plugins.remove(id)
+  }
+
+  def repositoryMenus   : List[RepositoryMenu] = plugins.values.flatMap(_.repositoryMenuList).toList
+  def globalMenus       : List[GlobalMenu]     = plugins.values.flatMap(_.globalMenuList).toList
+  def repositoryActions : List[Action]         = plugins.values.flatMap(_.repositoryActionList).toList
+  def globalActions     : List[Action]         = plugins.values.flatMap(_.globalActionList).toList
+
+  // Case classes to hold plug-ins information internally in GitBucket
   case class GlobalMenu(label: String, url: String, icon: String, condition: Context => Boolean)
   case class RepositoryMenu(label: String, name: String, url: String, icon: String, condition: Context => Boolean)
   case class Action(path: String, function: (HttpServletRequest, HttpServletResponse) => Any)
 
-  def addRepositoryMenu(label: String, name: String, url: String, icon: String)(condition: Context => Boolean): Unit = {
-    repositoryMenuList += RepositoryMenu(label, name, url, icon, condition)
-  }
+  /**
+   * This is a plug-in definition class.
+   */
+  class Plugin {
 
-  def addRepositoryMenu(label: String, name: String, url: String, icon: String, condition: ScriptObjectMirror): Unit = {
-    repositoryMenuList += RepositoryMenu(label, name, url, icon, (context) => condition.call(this, context).asInstanceOf[Boolean])
-  }
+    private[PluginSystem] val repositoryMenuList   = ListBuffer[RepositoryMenu]()
+    private[PluginSystem] val globalMenuList       = ListBuffer[GlobalMenu]()
+    private[PluginSystem] val repositoryActionList = ListBuffer[Action]()
+    private[PluginSystem] val globalActionList     = ListBuffer[Action]()
 
-  def addGlobalMenu(label: String, url: String, icon: String)(condition: Context => Boolean): Unit = {
-    globalMenuList += GlobalMenu(label, url, icon, condition)
-  }
+    def addRepositoryMenu(label: String, name: String, url: String, icon: String)(condition: Context => Boolean): Unit = {
+      repositoryMenuList += RepositoryMenu(label, name, url, icon, condition)
+    }
 
-  def addGlobalMenu(label: String, url: String, icon: String, condition: ScriptObjectMirror): Unit = {
-    globalMenuList += GlobalMenu(label, url, icon, (context) => condition.call(this, context).asInstanceOf[Boolean])
-  }
+    def addRepositoryMenu(label: String, name: String, url: String, icon: String, condition: ScriptObjectMirror): Unit = {
+      repositoryMenuList += RepositoryMenu(label, name, url, icon, (context) => condition.call(this, context).asInstanceOf[Boolean])
+    }
 
-  def addGlobalAction(path: String)(function: (HttpServletRequest, HttpServletResponse) => Any): Unit = {
-    globalActionList += Action(path, function)
-  }
+    def addGlobalMenu(label: String, url: String, icon: String)(condition: Context => Boolean): Unit = {
+      globalMenuList += GlobalMenu(label, url, icon, condition)
+    }
 
-  def addGlobalAction(path: String, function: ScriptObjectMirror): Unit = {
-    globalActionList += Action(path, (request, response) => function.call(this, request, response))
-  }
+    def addGlobalMenu(label: String, url: String, icon: String, condition: ScriptObjectMirror): Unit = {
+      globalMenuList += GlobalMenu(label, url, icon, (context) => condition.call(this, context).asInstanceOf[Boolean])
+    }
 
-  def addRepositoryAction(path: String)(function: (HttpServletRequest, HttpServletResponse) => Any): Unit = {
-    repositoryActionList += Action(path, function)
-  }
+    def addGlobalAction(path: String)(function: (HttpServletRequest, HttpServletResponse) => Any): Unit = {
+      globalActionList += Action(path, function)
+    }
 
-  def addRepositoryAction(path: String, function: ScriptObjectMirror): Unit = {
-    repositoryActionList += Action(path, (request, response) => function.call(this, request, response))
+    def addGlobalAction(path: String, function: ScriptObjectMirror): Unit = {
+      globalActionList += Action(path, (request, response) => function.call(this, request, response))
+    }
+
+    def addRepositoryAction(path: String)(function: (HttpServletRequest, HttpServletResponse) => Any): Unit = {
+      repositoryActionList += Action(path, function)
+    }
+
+    def addRepositoryAction(path: String, function: ScriptObjectMirror): Unit = {
+      repositoryActionList += Action(path, (request, response) => function.call(this, request, response))
+    }
   }
 
   def evaluateJavaScript(script: String): Any = {
     val engine = new ScriptEngineManager().getEngineByName("JavaScript")
     logger.debug("Script: " + script)
     engine.put("PluginSystem", this)
-    val result = engine.eval(script)
+    // TODO Support both of Nashorn and Rhino!
+    val result = engine.eval("var Plugin = Java.type(\"plugin.PluginSystem.Plugin\"); " + script)
     logger.debug("Result: " + result)
     result
   }
 
-  def repositoryMenus: List[RepositoryMenu] = repositoryMenuList.toList
-  def globalMenus: List[GlobalMenu] = globalMenuList.toList
-  def repositoryActions: List[Action] = repositoryActionList.toList
-  def globalActions: List[Action] = globalActionList.toList
 
   // TODO This is a test
-  addGlobalMenu("Google", "http://www.google.co.jp/", "data:image/png;base64,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")
-    { context => context.loginAccount.isDefined }
-
-  addRepositoryMenu("Board", "board", "/board", "data:image/png;base64,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")
-    { context => true}
-
-  addGlobalAction("/hello"){ (request, response) =>
-    "Hello World!"
-  }
+//  addGlobalMenu("Google", "http://www.google.co.jp/", "data:image/png;base64,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")
+//    { context => context.loginAccount.isDefined }
+//
+//  addRepositoryMenu("Board", "board", "/board", "data:image/png;base64,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")
+//    { context => true}
+//
+//  addGlobalAction("/hello"){ (request, response) =>
+//    "Hello World!"
+//  }
 
 }