Out of the box Visual Studio 2010 supports extensions development only for VS 2010 and Visual Studio 11 supports extensions development only for VS 11. If your Visual Studio extension supports both VS 2010/VS 11 and doesn’t contain much version specific code you may want to develop it in Visual Studio 2010 and just specify that it supports Visual Studio 11 as well.

Normally you specify what Visual Studio versions and editions your extension supports in the Select Visual Studio Version and Edition dialog available in the manifest designer:

But this dialog in Visual Studio 2010 doesn’t let you specify Visual Studio 11 support. You have to modify the manifest manually. Open source.extension.vsixmanifest in the code editor by selecting View – Code from the designer view and add the Visual Studio 11.0 tag copying the existing Visual Studio 10.0 tag:

<VisualStudio Version="11.0">
  <Edition>Pro</Edition>
</VisualStudio>

Specifying only the Pro edition means that the Premium and Ultimate editions are also supported. Additionally you can increase the MaxVersion attribute of SupportedFrameworkRuntimeEdition from 4.0 to 4.5. For Visual Studio 11 extensions default framework version is 4.5, but extensions with specified max version 4.0 work in VS 11 just fine in practice.

That’s all. Your extension can now be installed in both Visual Studio 2010 and Visual Studio 11.