View source for Start debugging multiple projects

Right-click the Solution in the Solution Explorer, and select Properties.  Go to the Common Properties – Startup Project page (it’s the first page in the dialog).

You’ll see three radio buttons:

* '''Current selection''' – whichever project had the inactive selection (i.e. whatever was selected previously) when you went to the solution property pages.
* '''Single startup project''' – usually this is the first project you had in the solution, or the project that you manually set as the startup project
* '''Multiple startup projects''' – and there was great joy.  When enabled, you can then pick and choose which projects to start (and make sure you choose Start and not Start without debugging)