A discipline that applies agile values and principles to the process of modelling
This is not a full methodology, but a set of practices, principles etc. that can be used to augment other Agile methodologies, and indeed other less agile approaches. AgileModeling was introduced by Scott Ambler and is supported by a book, a website and a particularly interesting forum that one may subscribe to via the website. Note the American spelling in the name.
AgileModeling, in brief, is modelling just enough to take the process forward. The need for complete and detailed models for mandatory documentation does not preclude the practices of AgileModeling. Consider employing a MercenaryAnalyst, or doing the documentation later, once the design is stable.