Facebook (stylized as facebook) is an American online social media and social networking service based in Menlo Park, California, and a flagship service of the namesake company Facebook, Inc. It was founded by Mark Zuckerberg, along with fellow Harvard College students and roommates Eduardo Saverin, Andrew McCollum, Dustin Moskovitz, and Chris Hughes.

The founders of Facebook initially limited membership to Harvard students. Membership was expanded to Columbia, Stanford, and Yale before being expanded to the rest of the Ivy League, MIT, and higher education institutions in the Boston area, then various other universities, and lastly high school students. Since 2006, anyone who claims to be at least 13 years old has been allowed to become a registered user of Facebook, though this may vary depending on local laws. The name comes from the face book directories often given to American university students.