Games are played whenever people interact, wherever there are strategies to adopt and outcomes or prizes to win. And that means games are played everywhere: from economics to evolutionary biology, from prison escapes to online poker, and from romantic liaisons to Cold War stand-offs.

Game theory is the study of such games — what happens when they are played rationally, and how we can predict their outcomes. This lively Very Short Introduction shows how game theory can be understood without mathematical equations, and how, from one simple premise, there springs a remarkably rich theory that has already had a profound effect on the sciences, and may yet revolutionize disciplines as far apart as psychology, ethics, and politics.