 <p>The play button is the start debugging feature. </p> <p>Yes, Visual Studio will ask every project in the solution to build at that point. But note asking to build and actually building are different things. Asking to build merely says, about to do something build again if you would like. MsBuild will then do a bit of checking under the hood and decide if it should actually build the underlying project.</p> <p>If your project is actually building then there may be some other problem going on. Can you give us some more info like language, project type, etc ...</p>