From job applications to selling goods or playing poker, there are many situations in which a strategic decision maker has only some, but not all the payoff-relevant information. Uninformed players then maximize their utility according to their beliefs about the unknown quantity. This course provides the tools to describe such incomplete information games and introduces commonly used solution concepts. In addition to the static environment, we study mechanism design, where the principal designs the environment, and dynamic/repeated environments, where players have the ability to learn over time.