The aim of this book is to provide a unified treatment of the non-interleaving approach to process semantics (as opposed to the interleaving approach of the process algebraists). Many results found in this book are collected for the first time outside conference and journal articles on the mathematics of non-interleaving semantics. It aims to give the reader a unified view of various attempts to model parallelism within one conceptual framework. It is aimed at postgraduates in theoretical computer science and academics who are teaching and researching in the modelling of discrete, concurrent or distributed systems. Workers in the information technology industry who are interested in available theoretical studies on parallelism should also be interested in this book.