This collection of essays is devoted to the semantics of concurrency. The papers are of two kinds: surveys and tutorials introducing the subject to novices and students and giving updates of the state of the art, and research papers presenting recent achievements in the semantics of concurrency. The contributors explore the connections, similarities and differences between various approaches to the semantics of concurrency, such as pomsets and metric semantics, event structures, synchronization trees, fix-points and languages, traces, CCS and Petri nets, and categorical models. They also...