This article show how communication through language can be expressed in terms of game theory. The general idea and the main line of argumentation is based on David Lewis’ book Convention (Lewis 1969) and more recent works on game theory that develop the concepts of cooperation and equilibrium. The term agreement, in the sense given to it by game theory, is used to show how to justify the thesis of the conventional nature of language. In the first part of the article some general notions of game theory are presented. Game theory is supposed to examine strategies chosen by rational agents in order to obtain preferred outcomes and is thus a good tool for describing and predicting human behaviour. It applies to situations when subjects operate reasonably, taking into account the behaviour of other rational subjects, and thus can also be used in situations of language communication. Sustaining conventionalism with game theory is possible primarily because it satisfies two basic conditions: it is both a description and a justification. Only within a complex system is it possible to explain the normative character of language, which, like utility, is only a simplified scheme. Through the analysis of coordination problems and the use of the principles of rationality and utility, it is possible to anticipate the behaviour of agents. In this context normativeness should be regarded as striving for balance, and even if another way of understanding is a deviation of the system, it still can be explored and explained within it.