Sporting contests have provided mass entertainment throughout history, and today generate revenues of approximately $200 billion annually in the US alone.  Like in the entertainment industry, the modern sports industry’s revenues are based on the entertainment value of output and more entertaining sporting contests imply greater game-day attendance, television revenues and sales of merchandise. Research by economists has attempted to understand and explain behavior as it relates to sporting contests, showing that standard microeconomic theory used to explain consumer and producer behavior can also be applied to the behavior of fans, team owners, league executives and players. One commonality among many ancient and modern sports is the existence of violence and aggression in contests. Compare, for example, a modern NASCAR race with a Roman chariot race: Only the technology has changed. From the perspective of an economist, violence in sporting contests is an outcome of the forces of supply and demand, and the phenomenon exists because fans respond to it.  Spectator preferences for violence bid up the monetary return to this behavior, and the rational response is a more violent or aggressive output.   The optimum level of violent or aggressive play in sporting contests is an empirical issue and this book contains chapters on violence and aggression in sports, concentrating on the reasons for the existence and persistence of such behavior.  Following a chapter devoted to the history of violence and aggression in sports, subsequent chapters are designed to cover the breadth of international professional sports including American football, soccer, ice hockey, basketball, baseball, auto racing, and fighting sports. Each chapter will contain econometric analysis of violence and aggressive play in a given sport. The individual chapters will examine whether or not a given sports league or governing body should intervene to reduce violence, and where intervention is warranted, extent of appropriate interventions is evaluated.  In addition to academics and students concerned with the economics and history of sport, the book’s emphasis on policies at the league and governing-body levels means this book will also be of interest representatives of those institutions.