Concurrent and distributed processes occur everywhere: in embedded systems, in information networks and databases, and in the form of applets roaming around on the World-Wide-Web. This book presents and develops state-of-the-art validation techniques for detecting safety violations; the focus is on the correctness of techniques that suffice for fully automatic validation of key components of such systems. It builds on and extends the notion of types, popular in many sequential programming languages as a technique for catching certain kinds of errors already at program development time, by incorporating behaviours (or structured effects) that are able to track the information flow in the presence of procedures, channel based communication, and the dynamic creation of network topologies. The technical development is performed for a language based on Concurrent ML.