Within the rapidly-growing arena of 'virtual worlds', such as Massively Multiplayer Online Games (MMOs), individuals behave in particular ways, influence one another, and develop complex relationships. This setting can be a useful tool for modeling complex social systems, cognitive factors, and interactions between groups and within organizations. To study these worlds effectively requires a cross-disciplinary approach that integrates social science theories with big data analytics. This broad-based book offers a comprehensive and holistic perspective on the field. It brings together research findings from an international team of experts in computer science (artificial intelligence, game design, and social computing), psychology, and the social sciences to help researchers and practitioners better understand the fundamental processes underpinning social behavior in virtual worlds such as World of Warcraft, Rift, Eve Online, and Travian.