Crystalline thin films have mechanical properties that cannot be predicted based on bulk scaling laws. Owing to their importance in technology, a great deal of effort has gone into modeling and simulation of the behaviors of dislocations in thin films. In this review, the successes and failures of modeling dislocations in thin films via analytical techniques, 2D dislocation dynamics simulations, and 3D discrete dislocation dynamics (DDD) simulations are discussed. Brief discussions of phase field models and level set methods are also included. The unique importance of 3D DDD simulations is highlighted, as these simulations allow study of realistic dislocation behavior that is otherwise difficult or impossible to observe. The utility of 3D DDD in discovering the mechanisms that control deformation in films is demonstrated, and first steps towards construction of a strain hardening model based on those mechanisms are described. (C) 2009 Elsevier Ltd. All rights reserved.