Competition is an intriguing and worrisome concept, sometimes perceived as a healthy emulation and sometimes as a form of Darwinism. Economic analysis provides a useful and rigorous guide to overcoming these oversimplified views by showing that competition is a mechanism for eliminating unjustified rents. This book presents the two main economic visions of competition (competition as a state versus as a process), but also its microeconomic and macroeconomic effects (notably on productivity and employment), the obstacles to its effectiveness, and the policies for opening up and regulating competition.