Social network analysis has a long history in sociology, but interest in this topic has broadened dramatically since 1995. This article reviews the origins and key concepts from the sociological literature on social networks, and outlines the network approach to economic behaviour (see Zuckerman, 2003 or White, 2002 for a broader vision of ‘economic networks’ not covered here due to space limitations). The central themes we trace relate to ‘social embeddedness’ and aggregation – how occupying different positions in complex networks enables and constrains action, as well as the resulting properties of global networks that arise from these actions.