diff --git a/core/src/main/java/hudson/PluginManager.java b/core/src/main/java/hudson/PluginManager.java
index fb427cbe1ae5810326051259e3e4344dc1d345b9..319c825a74a3b1ac0bb6388fafb5152a827c81e4 100644
--- a/core/src/main/java/hudson/PluginManager.java
+++ b/core/src/main/java/hudson/PluginManager.java
@@ -80,6 +80,16 @@ public final class PluginManager {
                 LOGGER.log(Level.SEVERE, "Failed to load a plug-in " + arc, e);
             }
         }
+
+        for (PluginWrapper p : activePlugins.toArray(new PluginWrapper[0]))
+            try {
+                p.load(this);
+            } catch (IOException e) {
+                failedPlugins.add(new FailedPlugin(p.getShortName(),e));
+                LOGGER.log(Level.SEVERE, "Failed to load a plug-in " + p.getShortName(), e);
+                activePlugins.remove(p);
+                plugins.remove(p);
+            }
     }
 
     public List<PluginWrapper> getPlugins() {
diff --git a/core/src/main/java/hudson/PluginWrapper.java b/core/src/main/java/hudson/PluginWrapper.java
index 83d136b63d8d8e3181810d1900e827ef420fd0bd..70c720fb80b8721ee161e88741e54637a4524655 100644
--- a/core/src/main/java/hudson/PluginWrapper.java
+++ b/core/src/main/java/hudson/PluginWrapper.java
@@ -56,7 +56,7 @@ public final class PluginWrapper {
      * Loaded plugin instance.
      * Null if disabled.
      */
-    public final Plugin plugin;
+    private Plugin plugin;
 
     /**
      * {@link ClassLoader} for loading classes from this plugin.
@@ -82,6 +82,27 @@ public final class PluginWrapper {
      */
     private final String shortName;
 
+    /**
+     * True if this plugin is activated for this session.
+     * The snapshot of <tt>disableFile.exists()</tt> as of the start up.
+     */
+    private final boolean active;
+
+    private final File archive;
+
+    private final List<Dependency> dependencies = new ArrayList<Dependency>();
+
+    private static final class Dependency {
+        public final String shortName;
+        public final String version;
+
+        public Dependency(String s) {
+            int idx = s.indexOf(':');
+            this.shortName = s.substring(0,idx);
+            this.version = s.substring(idx+1);
+        }
+    }
+
     /**
      * @param archive
      *      A .hpi archive file jar file, or a .hpl linked plugin.
@@ -92,6 +113,7 @@ public final class PluginWrapper {
      */
     public PluginWrapper(PluginManager owner, File archive) throws IOException {
         LOGGER.info("Loading plugin: "+archive);
+        this.archive = archive;
 
         this.shortName = getShortName(archive);
 
@@ -161,15 +183,33 @@ public final class PluginWrapper {
         disableFile = new File(archive.getPath()+".disabled");
         if(disableFile.exists()) {
             LOGGER.info("Plugin is disabled");
-            this.plugin = null;
-            return;
+            this.active = false;
+        } else {
+            this.active = true;
         }
 
+        // compute dependencies
+        String v = Util.fixNull(manifest.getMainAttributes().getValue("Plugin-Dependencies"));
+        for(String s : v.split(","))
+            dependencies.add(new Dependency(s));
+    }
+
+    /**
+     * Loads the plugin and starts it.
+     *
+     * <p>
+     * This should be done after all the classloaders are constructed for
+     * all the plugins, so that dependencies can be properly loaded by plugins.
+     */
+    /*package*/ void load(PluginManager owner) throws IOException {
         String className = manifest.getMainAttributes().getValue("Plugin-Class");
         if(className ==null) {
             throw new IOException("Plugin installation failed. No 'Plugin-Class' entry in the manifest of "+archive);
         }
 
+        if(!active)
+            return;
+
         // override the context classloader so that XStream activity in plugin.start()
         // will be able to resolve classes in this plugin
         ClassLoader old = Thread.currentThread().getContextClassLoader();
@@ -248,6 +288,13 @@ public final class PluginWrapper {
         return shortName;
     }
 
+    /**
+     * Gets the instance of {@link Plugin} contributed by this plugin.
+     */
+    public Plugin getPlugin() {
+        return plugin;
+    }
+
     @Override
     public String toString() {
         return "Plugin:" + getShortName();
@@ -321,7 +368,7 @@ public final class PluginWrapper {
      * Returns true if this plugin is enabled for this session.
      */
     public boolean isActive() {
-        return plugin!=null;
+        return active;
     }
 
     /**
diff --git a/core/src/main/java/hudson/model/Hudson.java b/core/src/main/java/hudson/model/Hudson.java
index f19afd80601c9b9ae0e699d69f39a4d9c498d218..2382dc0bffe4c6a6fcbedcc626a36009d53a8737 100644
--- a/core/src/main/java/hudson/model/Hudson.java
+++ b/core/src/main/java/hudson/model/Hudson.java
@@ -309,7 +309,7 @@ public final class Hudson extends View implements ItemGroup<TopLevelItem>, Node
     public Plugin getPlugin(String shortName) {
         PluginWrapper p = pluginManager.getPlugin(shortName);
         if(p==null)     return null;
-        return p.plugin;
+        return p.getPlugin();
     }
 
     /**