**Game theory** is a branch of mathematics, most commonly applied in economics, that studies situations in which players' outcomes are determined by their own choices as well as the choices of other players. It provides a formal approach to the study of strategic behavior and extends the simpler optimisation approach developed in neoclassical economics. Game theory can be viewed as a branch of decision theory in which players of the game interact with each other. A common example of game theory is the prisoner's dilemma.

Game theory was developed in 1944, by John von Neumann and Oskar Morgenstern, and was popularized in the 2001 film *A Beautiful Mind*, staring Russell Crowe as mathematician John Forbes Nash.