Hybrid systems are networks of interacting digital andanalog devices. Control systems for inherently unstableaircraft and computer aided manufacturing are typicalapplications for hybrid systems, but due to the rapiddevelopment of processor and circuit technology modern carsand consumer electronics use software to control physicalprocesses. The identifying characteristic of hybrid systemsis that they incorporate both continuous components governedby differential equations and also digital components -digital computers, sensors, and actuators controlled byprograms.This volume of invited refereed papers is inspired by aworkshop on the Theory of Hybrid Systems, held at theTechnical University, Lyngby, Denmark, in October 1992, andby a prior Hybrid Systems Workshop, held at CornellUniversity, USA, in June 1991, organized by R.L. Grossmanand A. Nerode. Some papers are the final versions of paperspresented at these workshops and some are invited papersfrom other researchers who were not able to attend theseworkshops.