The Iterated Prisoner's Dilemma (IPD) is widely regarded as a standard model for the evolution of cooperation. This review tries to give an outline of the development in the field since Axelrod and Hamilton (1981) spawned an avalanche of papers with the announcement of Tit-for-tat as the winner of their computer tournament. The most important advancements in the game-theoretical work on different aspects of the game are described. It becomes evident that changing any of the numerous parameters of the game will inevitably change the outcome; there is virtually no end to the IPD. Using experimental data from various taxa, the applicability of the IPD in nature is analysed and potential future developments in the area are discussed.