There are two well-developed theories that characterize what it means to make choices rationally. One is Decision Theory, which considers the position of one agent choosing among alternatives, with varying information about factors that might influence the resulting outcomes. The other is Game Theory, which provides techniques for analyzing interactions among several agents. This first part of the course focuses on explaining the basic elements of these two theories and related concepts (such as probability and utility). Later topics include causal decision theory, infinite decision theory and evolutionary game theory. We will also consider applications to topics such as ethical and social theory, and the philosophy of science.