## 1.1: Introduction

Why? Many economic, political, and social interactions are shaped by the local structure of relationships: trade, sharing, transmission of viruses... Social networks influence behavior: crime, employment, human capital, voting, smoking.

#### Primary Questions:

- What do we know about network structure?
- How do networks form?
- How do networks influence behavior?

#### Central Focus: Models for Analyzing and Understanding Networks (Graph models)

- Provide insight: Why do social networks have short average path lengths?
- Comparative statics: How does component structure change with density?
- Predict out of sample: What will happen with a new policy?
- Is there significant clustering on a local level or did it appear at random?

## 1.2: Examples and Challenges

