On this occasion, they posted this photo (right) on their Wall, and wished the "1.5 million" people on Facebook who share their birthday.
Facebook launched in 2004 to Harvard students, later expanding to Stanford, Columbia, Dartmouth and Yale. Slowly, it opened up to more colleges. It was called TheFacebook.com In September 2005, a high-school version of the site was launched.
The social network opened later to everyone 13 and older with a valid email address exactly a year later.
And now, in 2011, they celebrate their 7th birthday.
Happy birthday, Facebook!
Update: They are moving their offices to Menlo Park .