In this document, we present the notion of a cost game, defined as a cooperative game where the gain from cooperation is the cost reduction obtained when the projects of a set of agents are realized in a coordinated way. The problem is then to decide how this gain will be shared among agents or similarly how the joint realization of the projects will be financed. We survey the different types of cost games and we introduce the notions of pre-solution and solution, as well as the usual properties that a solution should satisfy.