Gas-liquid flows, arising as it does out of Masters level and post experience courses, is particularly suitable for these audiences. However, book will also be a valuable source to researchers, not only to new readers coming to the subject for the first time, but also to those more experienced who will gain new insights from its contents. Amongst its aims are to bring together communality of features in two-phase flow across flow patterns and geometries and to put new material into the context of earlier work showing how early and later descriptions have a common root. The book introduces the basic methods used for two phase design methods, particularly for pressure drop. It goes on to introduce flow patterns and the physics of the transitions between them, and then examines the major flow patterns, concentrating on annular flow in vertical pipes. It finishes with chapters on geometries other than pipes, including pipe junctions.