diff --git a/install_action.h b/install_action.h
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--- /dev/null
+++ b/install_action.h
@@ -0,0 +1,86 @@
+// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROMEOS_PLATFORM_UPDATE_ENGINE_INSTALL_ACTION_H__
+#define CHROMEOS_PLATFORM_UPDATE_ENGINE_INSTALL_ACTION_H__
+
+#include "base/scoped_ptr.h"
+#include "update_engine/action.h"
+#include "update_engine/delta_diff_parser.h"
+#include "update_engine/install_plan.h"
+#include "update_engine/update_metadata.pb.h"
+
+// The Install Action is responsible for ensuring the update that's been
+// downloaded has been installed. This may be a no-op in the case of a full
+// update, since those will be downloaded directly into the destination
+// partition. However, for a delta update some work is required.
+
+// An InstallPlan struct must be passed to this action before PerformAction()
+// is called so that this action knows if it's a delta update, and if so,
+// what the paths are.
+
+// TODO(adlr): At the moment, InstallAction is synchronous. It should be
+// updated to be asynchronous at some point.
+
+namespace chromeos_update_engine {
+
+class InstallAction;
+class NoneType;
+
+template<>
+class ActionTraits<InstallAction> {
+ public:
+  // Takes the InstallPlan for input
+  typedef InstallPlan InputObjectType;
+  // On success, puts the output device path on output
+  typedef std::string OutputObjectType;
+};
+
+class InstallAction : public Action<InstallAction> {
+ public:
+  InstallAction() {}
+  typedef ActionTraits<InstallAction>::InputObjectType InputObjectType;
+  typedef ActionTraits<InstallAction>::OutputObjectType OutputObjectType;
+  void PerformAction();
+
+  // This action is synchronous for now.
+  void TerminateProcessing() { CHECK(false); }
+
+  // Debugging/logging
+  static std::string StaticType() { return "InstallAction"; }
+  std::string Type() const { return StaticType(); }
+
+ private:
+  // Installs 'file' into mountpoint. 'path' is the path that 'file'
+  // should have when we reboot and mountpoint is root.
+  bool InstallFile(const std::string& mountpoint,
+                   const DeltaArchiveManifest_File& file,
+                   const std::string& path,
+                   const DeltaDiffParser& parser) const;
+  // These are helpers for InstallFile. They focus on specific file types:
+  // Regular data files:
+  bool InstallFileRegularFile(const std::string& mountpoint,
+                              const DeltaArchiveManifest_File& file,
+                              const std::string& path,
+                              const DeltaDiffParser& parser,
+                              const bool exists) const;
+  // char/block devices, fifos, and sockets:
+  bool InstallFileSpecialFile(const std::string& mountpoint,
+                              const DeltaArchiveManifest_File& file,
+                              const std::string& path,
+                              const DeltaDiffParser& parser,
+                              const bool exists) const;
+  // symlinks:
+  bool InstallFileSymlink(const std::string& mountpoint,
+                          const DeltaArchiveManifest_File& file,
+                          const std::string& path,
+                          const DeltaDiffParser& parser,
+                          const bool exists) const;
+
+  DISALLOW_COPY_AND_ASSIGN(InstallAction);
+};
+
+}  // namespace chromeos_update_engine
+
+#endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_INSTALL_ACTION_H__