A large part of syntax is concerned with movement. Accordingly, one of the most central questions of syntax is why elements move at all, and why they move to certain specific positions. A powerful idea of current syntactic theorizing is that certain morpho-syntactic features must be checked by some element moving to their position and thereby act as triggers for movement. This book addresses the appropriateness of such an approach and discusses in detail the ways in which syntactic theory should deal with triggering mechanisms, what triggers should be allowed, and how a variety of constructions in more than a dozen languages can be adequately handled in terms of trigger theory.