This chapter reports authoritative insights into one of the most significant developments related to social interaction – social network sites – and offers an analytic framework for exploring these new sites, while underscoring the centrality of social interaction since the Internet's earliest days, such as through email. Social network sites (SNSs) presented several characteristics that made it possible for individuals to easily update their profiles. The implicit role of communication and information sharing has become the driving motivator for participation. The concept of ‘Web 2.0’ was an industry-driven phenomenon, hyped by the news media and by business analysts alike. Social network sites emerged out of the Web 2.0 and social media phenomena, mixing new technologies and older computer-mediated communication practices infused by tech industry ideals. Server-level data offer a unique opportunity to access elaborated behavioural data about what people are doing on SNSs.