Friends, family, and co-workers use Facebook to communicate with each other. Many businesses use the site to show their products. Users can write about themselves or their companies and include pictures and videos. They can also permit everyone, or only a few people, to see their Facebook pages.

This past summer, Facebook announced that it has over five hundred million active users around the world. About half of them use the site every day. About seventy percent of all Facebook users are in countries outside the United States.

Mark Zuckerberg and three friends started Facebook in two thousand four. He was a second year student at Harvard University in Massachusetts. He began the project by illegally using the university’s computer system. Harvard University charged him with violating several laws.

Mr. Zuckerberg was almost forced to leave school. But the university withdrew the charges. Mark Zuckerberg was also accused of stealing other people’s ideas and using them in Facebook. He has denied the charges. Several people have taken legal action against him.

At first, only Harvard students could use Facebook. But it quickly expanded to other universities. The website was also opened to high school students. Now, anyone at least thirteen years old with an e-mail address can join.

In the early days, only a small group of people managed Facebook. Now it has over one thousand seven hundred workers in twelve countries. Facebook makes money by selling advertising. It has been extremely successful. The financial company Second Market, Incorporated, says Facebook is worth forty-one billion dollars.

A movie about the creation of Facebook, called “The Social Network,” was released in October.