This book contains all full papers presented at ACRI 2000, the Fourth International Conference on Cellular Automata for Research and Industry, held at the University of Karlsruhe (Germany), 4 - 6 October, 2000. The continuation of and growing interest in research on Cellular Automata models for real world phenomena indicates the feasibility of this approach. A quick glance at the table contents of this book shows that results came from such different areas as biology, economics, physics, traffic flow and urban development. This work is complemented by contributions on the implementation and evaluation of software for Cellular Automata simulation, which is a necessary (but of course in no way sufficient) ingredient for the successful application of Cellular Automata. Applying Cellular Automata without trying to understand their behavior, in depth would be an unfortunate development. But as properties and power in earlier years it was again one of the strong points of ACRI to bring together researchers not only from different application areas but also from theory. Of course, this is reflected by the list of accepted contributions which also comprise theoretical papers and even papers which certainly belong to the intersection of several fields. Examples are the generation and recognition of geometrical patters and the influence of possible failures on the power of CA which obviously are of relevance also to applications.