This course is a course in decision theory that emphasizes axiomatic methods and mathematical analysis. It navigates not only through the traditional normative approach but also through more recent behavioral (i.e., descriptive) approaches to decision-making, incorporating psychological insights. We explore essential topics in decision theory such as dynamic choice, stochastic choice, ambiguity aversion, expected utility, and revealed preferences. This in-depth study provides students with a sophisticated understanding of the frameworks governing decision making, emphasizing the role of rigorous analysis and mentioning empirical evidence found in experimental economics and psychology. This course offers valuable insights into understanding individual behaviors across both economic and financial contexts as well as in broader scenarios, providing students with the mathematical proficiency required to analyze decision-making processes rigorously.