 Section 1 of the entry outlines the history and working definition of social networking services. Section 2 identifies the early philosophical foundations of reflection on the ethics of online social networks, leading up to the emergence of Web 2.0 standards (supporting user interactions) and full-fledged SNS. Section 3 reviews the primary ethical topic areas around which philosophical reflections on SNS have, to date, converged: privacy; identity and community; friendship, virtue and the good life; democracy, free speech, misinformation/disinformation and the public sphere; and cybercrime. Finally, Section 4 reviews some of the metaethical issues potentially impacted by the emergence of SNS.