Lecture, three hours; discussion, one hour. Requisites: courses 41, 101. In today's networked societies, everyone belongs to many social and economic networks. People and firms rely on various kinds of networks to interact with each other. As a result, the structure of networks affects and shapes behavior in a fundamental way. Study offers a framework in which to understand how agents behave and interact on networks, using tools from economics and statistics. Study of how to classify networks, what is special about social/economics networks, and how information  and misinformation can spread through networks, among others. Special emphasis on how the theory of social and economic networks informs and improves the traditional economic theory. P/NP or letter grading.