Facebook, Inc. is an American online social media and social networking service company based in Menlo Park, California, United States. The Facebook website was launched on February 4, 2004, by Mark Zuckerberg, along with fellow Harvard College students and roommates, Eduardo Saverin, Andrew McCollum, Dustin Moskovitz, and Chris Hughes.

The Facebook service can be accessed from devices with Internet connectivity, such as personal computers, tablets and smartphones. After registering, users can create a customized profile revealing information about themselves. They can post text, photos and multimedia which is shared with any other users that have agreed to be their "friend". Users can also use various embedded apps, join common-interest groups, and receive notifications of their friends' activities.

As of December 2018, Facebook had more than 2.3 billion monthly active users. Facebook is one of the world's most valuable companies. It is considered one of the Big Four technology companies along with Amazon, Apple, and Google.