This text addresses formal methods (FMs) applicable to the specification, verification, implementation, and testing of complex distributed systems and communication protocols. The early, pioneering phases in the development of formal methods, with their conflicts between evangelistic and skeptical attitudes, are essentially over. Many FMs have reached maturity, and a number of papers in this book report on successful experiences in specifying and verifying real distributed systems and protocols. The main topics covered are: model checking theory and applications; verification and theorem proving; testing theory and applications; multicast protocol analysis and simulation; hardware specification, implementation, and testing; and FMs for security.