Social sciences in general are an attempt to understand the ways in which people behave and make decisions, as individuals and in group settings. Decision and game theory provides a formal language to describe situations of conflict and cooperation between rational decision makers. Over the past decades, decision and game theory has become an indispensable tool in the social sciences and natural sciences, especially in economics, but also in political science, international relations, sociology, law, psychology, computer sciences and biology. Its influence and success has been recognized by multiple Nobel prizes in economics. This course will introduce students to the fundamentals of decision and game theory. We cover the basics of rational choice theory, single-person decision problems with and without risk, static games, Nash equilibrium, dynamic games with complete information, backwards induction, subgame-perfect Nash equilibrium, Bayesian Nash equilibrium, etc.. We will apply all these concepts to problems in various contexts such as international relations, economics, politics and law.