Chapter 1: Introduction

A network is a collection of nodes and edges, where an edge connects two nodes. Many social, natural and engineered systems can be represented as networks. Examples include friendship networks, international relationships, gene regulatory networks, food webs, airport networks and the Internet just to name a few. Since the late 1990s, our understanding of real networks, from large to small ones, has been significantly advanced with the integration of theoretical, computational and conceptual tools from statistical physics, computer science, engineering, mathematics and other domains. Many networks have been recognized to be complex but governed by beautiful and universal laws. Together with applications, this field of research can be collectively called network science…