Twitter: How it began and how much it is worth
7 November 2013 Last updated at 01:49 GMT
Newsnight's David Grossman looks at the history of Twitter as the company begins its first day of trading after listing on the New York Stock Exchange.
The giant microblogging site, founded just seven years ago, is worth more than $18bn.
Four young friends started Twitter but over its lifetime those friendships have broken down.