Game theory is the formal toolkit for analyzing situations in which payoffs depend not only on your actions (say, which TV series you watch), but also others' (whether your friends are watching the same show). You've probably already heard of some famous games, like the prisoners' dilemma and the costly signaling game. We'll teach you to solve games like these, and more, using tools like Nash equilibrium, subgame perfection, Bayesian Nash equilibrium, and the one-shot deviation principle.Game theory has traditionally been applied to understand the behavior of highly deliberate agents, like heads of state, firms in an oligopoly, or participants in an auction. However, we'll apply game theory to social behavior typically considered the realm of psychologists and philosophers, such as why we speak indirectly, in what sense beauty is socially constructed, and where our moral intuitions come from.There will be about six problem sets. These can be completed in groups. Tutorials are not required but are highly recommended for students without a substantial background in math. There will also be a final exam.