This chapter focuses on standard games. It starts by explaining how a standard game can be viewed as a collection of one-person decision problems. Subsequently, it is shown how belief hierarchies about choices can be visualized by means of a beliefs diagram, and mathematically encoded by means of an epistemic model with types. This is used to provide a formal definition of common belief in rationality – the central line of reasoning which states that a player believes that others choose rationally, believes that others believe that others choose rationally, and so on. It is shown that the choices which are possible under common belief in rationality can be characterized by the iterated elimination of strictly dominated choices.