This book describes methods and techniques for the design of software systems particularly reactive software systems that engage in stimulus-response behavior. Such systems, which include information systems, workflow management systems, systems for e-commerce, production control systems, and embedded software, increasingly embody design aspects previously considered alonesuch as complex information processing, non-trivial behavior, and communication between different components aspects traditionally treated separately by classic software design methodologies. But, as this book illustrates, the software designer is better served by the ability to intelligently pick and choose from among a variety of techniques according to the particular demands and properties of the system under development.