It is 7 years today since the first tweet was sent. 400 million are now sent every day from 500 million users world-wide.
Twitter was founded in San Francisco but is used by people in nearly every country in the world.
The service is available in more than 20 languages and the company says they are continuing to add more.
The user with the most followers is singer Justin Bieber. He has 36 million followers. While social media management company Hootsuite follows more than 1.1 million accounts - the most of any user.
The most followed brand on the site is YouTube with nearly 25 million followers.
So what do you make of Twitter's big day?
Today is World Poetry Day & it's also Twitter's birthday - so now's the time to air that poem you always had in you. Be 'creative'.... #iand
— Ian Dempsey(@IanDempsey) March 21, 2013
Happy Birthday to @twitter, 7 years old today.... Awwwwh!!!! #happybirthdaytwitter twitter.com/AmazingEarth_/…
— Amazing Earth (@AmazingEarth_) March 21, 2013
Twitter's 7th birthday today. Unlike some rivals, no signs of decline. Short = good. #140chars #Twitter7
— Adrian Weckler (@adrianweckler) March 21, 2013
