In game theory, a trigger strategy is any of a class of strategies employed in a repeated

non-cooperative game In game theory, a non-cooperative game is a game with competition between individual players, as opposed to cooperative games, and in which alliances can only operate if self-enforcing (e.g. through credible threats). However, 'cooperative' an ...

. A player using a trigger strategy initially cooperates but punishes the opponent if a certain level of defection (i.e., the trigger) is observed. The level of ''punishment'' and the sensitivity of the trigger vary with different trigger strategies.

Trigger strategies

* Grim trigger (the punishment continues indefinitely after the other player defects just once) *

Tit for tat Tit for tat is an English saying meaning "equivalent retaliation". It developed from "tip for tap", first recorded in 1558. It is also a highly effective strategy in game theory. An agent using this strategy will first cooperate, then subsequ ...

(the punishment continues as long as the other player defects) * Tit for two tats (a more forgiving variant of tit for tat)

References

;Textbooks and general reference texts * Vives, X. (1999) ''Oligopoly pricing'', MIT Press, Cambridge MA (readable; suitable for advanced undergraduates.) * Tirole, J. (1988) ''The Theory of Industrial Organization'', MIT Press, Cambridge MA (An organized introduction to industrial organization) ;Classical paper on this subject * Friedman, J. (1971). A non-cooperative equilibrium for supergames, Review of Economic Studies 38, 1–12. (The first formal proof of the Folk theorem (game theory)). Non-cooperative games {{Gametheory-stub