Facebook is a social networking website launched on February 4, 2004. The free-access website is privately owned and operated by Facebook, Inc. Users can join networks organized by city, workplace, school, and region to connect and interact with other people. People can also add friends and send them messages, and update their personal profile to notify friends about themselves. The website's name refers to the paper facebooks depicting members of a campus community that some American colleges and preparatory schools give to incoming students, faculty, and staff as a way to get to know other people on campus.

Mark Zuckerberg founded Facebook while still a student at Harvard University. Website membership was initially limited to Harvard students, but was expanded to other colleges in the Ivy League. It later expanded further to include any university student, then high school students, and, finally, to anyone aged 13 and over. Peter Thiel was the first person to fund the company, with an initial investment of US$500,000. Features include a Wall for posting messages and Photos for uploading digital photos. The website has more than 80 million active users worldwide.

Facebook has met with some controversy over the past few years. It has been blocked in several countries including Syria, China, and Iran. Privacy has also been an issue, and it has been compromised several times. It is also facing several lawsuits from a number of Zuckerberg's former classmates, who claim that Facebook had stolen their source code and other intellectual property.