These twenty-eight contributions report advances in one of the most active research areas in artificial intellgence. Qualitative modeling techniques are an essential part of building second generation knowledge-based systems. This book provides a timely overview of the field while also giving some indications about applications that appear to be feasible now or in the near future. Chapters are organized into sections covering modeling and simulation, ontologies, computational issues, and qualitative analysis. Modeling a physical system in order to simulate it or solve particular problems regarding the system is an important motivation of qualitative physics, involving formal procedures and concepts. The chapters in the section on modeling address the problem of how to set up and structure qualitative models, particularly for use in simulation. Ontology, or the science of being, is the basis for all modeling. Accordingly, chapters on ontologies discuss problems fundamental for finding representational formalism and inference mechanisms appropriate for different aspects of reasoning about physical systems. Computational issues arising from attempts to turn qualitative theories into practical software are then taken up. In addition to simulation and modeling, qualitative physics can be used to solve particular problems dealing with physical systems, and the concluding chapters present techniques for tasks ranging from the analysis of behavior to conceptual design. Boi Faltings is Associate Professor of Computer Science at the Swiss Federal Institute of Technology, Lausanne. Peter Struss is Head of the Advanced Reasoning Methods Group at Siemens Corporate Research and Development in Munich.