The course covers the basics of consumer and firm behavior, emphasizing the common structure of constrained optimization and the role of convexity. The foundations of utility maximization are discussed, as well as the paradigm of revealed preferences and its limitations. Using the concepts of indifference curves and budget sets, the marginality pr inciple is explained and consumer demand is analyzed. Important special cases include the supply of labor, inter-temporal demand, and uncertainty. Finally, the theory of the firm is presented as another manifestation of the general principles, including an analysis of the firm's optimal decision, and the derived supply and demand for production factors.