What makes social network sites unique is not that they allow individuals to meet strangers, but rather that they enable users to articulate and make visible their social networks. While networking is possible on these sites, it is not the primary practice on many of them, nor is it what differentiates them from other forms of computer-mediated communication (CMC). “Networking” emphasizes relationship initiation, often between strangers. We chose not to employ the term “networking” for two reasons: emphasis and scope. While we use the term “social network site” to describe this phenomenon, the term “social networking sites” also appears in public discourse, and the two terms are often used interchangeably. The nature and nomenclature of these connections may vary from site to site. We define social network sites as web-based services that allow individuals to (1) construct a public or semi-public profile within a bounded system, (2) articulate a list of other users with whom they share a connection, and (3) view and traverse their list of connections and those made by others within the system. We conclude with a description of the articles included in this special section and suggestions for future research. Following this, we review recent scholarship on SNSs and attempt to contextualize and highlight key works. We begin by defining what constitutes a social network site and then present one perspective on the historical development of SNSs, drawing from personal interviews and public accounts of sites and their changes over time. The purpose of this introduction is to provide a conceptual, historical, and scholarly context for the articles in this collection. By collecting these articles in this issue, our goal is to showcase some of the interdisciplinary scholarship around these sites. This special theme section of the Journal of Computer-Mediated Communication brings together a unique collection of articles that analyze a wide spectrum of social network sites using various methodological techniques, theoretical traditions, and analytic approaches. Scholars from disparate fields have examined SNSs in order to understand the practices, implications, culture, and meaning of the sites, as well as users’ engagement with them. Sites also vary in the extent to which they incorporate new information and communication tools, such as mobile connectivity, blogging, and photo/video-sharing. Some sites cater to diverse audiences, while others attract people based on common language or shared racial, sexual, religious, or nationality-based identities. Most sites support the maintenance of pre-existing social networks, but others help strangers connect based on shared interests, political views, or activities. While their key technological features are fairly consistent, the cultures that emerge around SNSs are varied. As of this writing, there are hundreds of SNSs, with various technological affordances, supporting a wide range of interests and practices. Since their introduction, social network sites (SNSs) such as MySpace, Facebook, Cyworld, and Bebo have attracted millions of users, many of whom have integrated these sites into their daily practices.