Lecture, three hours. Requisite: course 120A or 120B. Covers rational decision-making, how people deviate from this ideal, and how decision-making can be improved. Discussion of these topics for simple decisions that only affect the person who makes them, then revisited in the context of complex decisions that affect multiple stakeholders differently. Includes topics such as (in)effective altruism, societal decision-making, and social dilemmas. May be repeated once for credit. P/NP or letter grading.