I can think of some very legitimate reasons why it would be a good idea to have controllers in a separate assembly. Consider an environment where you have multiple different apps with *completely* different interfaces and UI requirements that share the same Controller logic. In such a case, it would be a VERY valid scenario to put controllers in a separate assembly that could be shared between projects. I'm currently working in such an environment.

aspevia

"Controllers in an MVC are used to create UIs."

That's a first for me. The "V" in MVC stands for "View" ... which *is* the UI for an MVC application, not the Controller. Unless there is a compelling need to extract it and place it somewhere else (often times, the Model is more appropriate), the Controller *is* where I put much, if not all, of the business logic in my MVC apps.

With that out of the way ... I think the original question is a very legitimate one, and I'd love to know the answer to it.