First and foremost it’s important to note that only ReSharper version 7 and higher works with Visual Studio 2012 and also that Resharper 8 and above works with Visual Studio 2013.
Now, I came across the problem that I installed ReSharper 7 for Visual Studio 2010 some time ago. I installed Visual Studio 2012 afterwards and ReSharper was not available in VS2012 (you can check if ReSharper is integrated into your Visual Studio by simply checking if the ReSharper menu item is available in the top menu bar or go to the Help menu item in Visual Studio and click on About Microsoft Visual Studio to check the Installed Products list).
After some digging around, I figured out how to enable ReSharper for VS2012 without having to re-install it:
1. Go to Control Panel, select Programs and Features
2. Select JetBrains ReSharper and click on Change
3. The ReSharper Setup main dialog will appear, here click on Change
4. The ReSharper Setup integration options dialog will appear, check the Visual Studio 2012 checkbox and click on Install
Done!
Same steps apply for ReShaper 8 and Visual Studio 2013 but obviously VS2013 has to be checked at step 4.
This might seem obvious looking back now but it didn’t seem so easy without knowing these exact steps. I was looking in all the wrong places! 🙂
FitGeekGirl 
Bravo! I wasted almost one hour to figure out where to do it. Thanks for the article.