In a web-based application that uses the Model-View-Controller design pattern, the logic relating to processing form submissions seems to belong somewhere in between the Model layer and the Controller layer. This is especially true in the case of a complex form (i.e. where form processing goes well beyond simple CRUD operations).

What's the best way to conceptualize this? Are forms simply a kind of glue between models and controllers? Or does form logic belong squarely in the M or C camp?

EDIT: I understand the basic flow of information in an MVC application (see chills42's answer for a summary). My question is where the form processing logic belongs - in the controller, in the model, or somewhere else?