This text focuses on the practical viewpoint of customer behaviour and its effect on the performance of the queueing system. The book's objectives are threefold: It is a comprehensive survey of the literature on equilibrium behavior of customers and servers in queueing systems. The literature is rich and considerable, but lacks continuity. This book should provide continuity and cover some issues that have not been adequately treated. In addition, it will examine the known results of the field, classify them and identify where and how they relate to each other. Finally, it seeks to fill a number of the gaps in the literature with results while explicitly outlining open problems in other areas. With this book, it is the authors' paramount purpose is to motivate further research and to help researchers identify new and interesting open problems.