Originally, the research reported in this book was motivated by the way the material used for an introductory course on Distributed Computing (taught in the spring of 1985) was presented in the literature. The teacher of the course, Jan van Leeuwen, and I felt that many results were presented in a way that needed clarifying, and that correctness proofs, if existent, were often far from convincing, if correct at all. Thus we started to develop correctness proofs for some distributed protocols. Gradually a methodology emerged for such proofs, based on the idea of “protocol skeletons” and “system-wide invariants”. Similar ideas were developed by others in the context of formal proof systems for parallel and distributed programs.

I thank the ESPRIT Basic Research Action No. 7141 (project ALCOM II: Algorithms and Complexity), the Netherlands Organization for Scienctific Research (NWO) under contract NF 62-376 (NFI project ALADDIN: Algorithmic Aspects of Parallel and Distributed Systems), and the Department of Computer Science at Utrecht University for giving me the opportunity to do research on this topic, and for providing such a stimulating environment. I thank my coauthors Jan van Leeuwen, Hans Bodlaender, and Gerard Tel, and also Petra van Haaften, Hans Zantema, and Netty van Gasteren for all the discussions we had.

Later the idea came up to write a thesis about this subject, and I especially thank my thesis advisor Jan van Leeuwen for his stimulating support. The first four chapters of the thesis served as preliminary versions for the first four chapters of this book, while chapter 5 on commit protocols was added later.