>That is the question.
>
>No really. What is the difference between Build and Rebuild?

It depends on how you configure VS.NET when you have a solution with multiple projects on it. This is what the MSDN says:

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Build
Builds only those project items for the selected combinations of project configuration and platform that have changed since the last build.

Rebuild
Does a complete build from scratch of all items for the selected project items for the selected combinations of project configuration and platform.
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I've noticed that on large solutions with a lot of project dependencies Rebuild does take longer. But to be honest, I have never analyzed what gets re-built that wouldn't under build.