Game Theory aims to help us understand situations in which decision-makers interact. It has become a standard methodology in Economics. This course provides a rigorous introduction to the main concepts of Game Theory and its applications. It covers the standard ways of representing games and the main concepts to analyze static and dynamic strategic settings, with complete or incomplete information. It also covers some of the most important economic applications of game-theoretic reasoning, including competition in oligopolistic markets, trade policy, bargaining, contracting situations, auctions, and signaling in labor markets.