This book constitutes the thoroughly refereed post-conference documentation of the Fourth International Conference on Hybrid Systems held in Ithaca, NY, USA, in October 1996. The volume presents 19 carefully revised full papers selected from numerous submissions. Hybrid systems research focuses on modeling, design, and validation of interacting systems (plants) and computer programs (control automata). This volume is devoted to hybrid systems models, formal verification, computer simulation, goal reachability, algorithms for extracting hybrid control programs, and application models for avionics, highway traffic control, and air traffic control.