Xcode 6 - Main.storyboard only showing up as source code, Interface Builder missing

As so many people have pointed out, right-click on the file and hover over Open As and select Default - Interface Builder.

However, if this is not an option for you because Open As shows <None>, make sure you are in the standard editor and not the version editor. Go up to View in XCode menu --> view --> hover over Standard Editor and select Show Standard Editor. Now repeat the steps others have suggested and you should get the results you're looking for.

change to Standard Editor by clicking 'Command + Enter' key . Then Main.storyboard may show as Interface Builder.

I had the same issue, where "Open As" wasn't an option on the main storyboard, and xibs were also showing as XML.

The solution that worked for me was to right click on an xib which did have the "Open as --> Interface Builder" option. Then, I went back to storyboard, and the main storyboard showed up properly.