Facebook is a social networking site where members can maintain a user profile, add friends and interact with them using social tools and applications, and join networks based on location, company, school, region, etc. Founded by Mark Zuckerberg while a student at Harvard, membership was originally restricted only within the campus. Eventually the site expanded to open membership to other colleges, followed by high school students, and eventually to anyone of at least 13 years of age.

Currently boasting over 200 million users around the world, Facebook is one of the most popular social networks. The site and its executive leadership have weathered many controversies surrounding international blocks, being banned in certain workplaces, privacy issues, security breaches, lawsuits from former Zuckerberg classmates, unpopular changes to the Terms of Service and several redesigns.

Facebook differs from rival social hub site MySpace in that the former puts more emphasis on networking and interactivity between users, while the latter offers more under-the-hood customization of a personal profile web pages with custom graphics and music using HTML. Among the most noteworthy Facebook features is an optional automatic news feed, which displays updates for all connected Friends and Groups. Also prominent is the unlimited capacity to upload photos, and organize them into albums for profile visitors to view. The most iconic and popular Facebook feature is the Wall, on which visitors to a user's profile can post messages visible to all other visitors. The depth of personal information and constant stream of status updates has sometimes run afoul of privacy concerns, bringing about the term "Facebook stalking." In response, the site implemented various layers of privacy settings, enabling users to make various features or their entire profile available only to some or all of their Friend lists, instead of completely public. One last defining element of Facebook is the Facebook Applications platform that allows third parties to write custom bits of software that members can plug into their profile pages. Facebook apps range from simple utilities to tie-ins with other site profiles to casual games and a wide selection of video and other media apps.