avoid delving into particular applications. The primary intention is to present general mathematical models that describe the principal kinds of coopera­ tive behavior in distributed active systems. Simple examples, ranging from chemical physics to economics, serve only as illustrations of the typical context in which a particular model can apply. The manner of exposition is more in the tradition of theoretical physics than of in mathematics: Elaborate fonnal proofs and rigorous estimates are often replaced the text by arguments based on an intuitive understanding of the relevant models. Because of the interdisciplinary nature of this book, its readers might well come from very diverse fields of endeavor. It was therefore desirable to minimize the re­ quired preliminary knowledge. Generally, a standard university course in differential calculus and linear algebra is sufficient.