UPDATE: Since people keep posting here to bring the post back up to the top: the problems in the original post were all gone for me some time during 2016. This might've been a fluke, but in case it's consistent, I'll post this: Upgrading to Unity 5.2 broke VS Tools for Unity for me - VS tools was unselectable in the External Script Editor drop-down, and opening any script caused MonoDevelop to open and promptly fail to load anything if "normal" visual studio was selected. All of this was fixed by simply deleting the VS tools folder from the Assets folder of the project. It seems like having both the new built-in VS tools and the old .dll causes both of them to fail hard. Big props to the dev team for adding VS tools as a standard feature in Unity. EDIT: As you can see by following this thread, the UnityVS integration isn't quite there. There are some instances where integration used to work in 5.1 + UnityVS, where it doesn't work anymore. The known problems are: Users of the Resharper plugin cannot open scripts from Unity without first opening Visual Studio manually Mac users running Visual Studio on a VM doesn't have working integration It may seem like other plugins can also cause the integration to fail.