Timeline of Twitter's history
Twitter, the microblogging site that's made people communicate in 140 characters, started publicly trading on Nov. 7, more than seven years after its birth. Its users has grown from a small group of active users to more than 200 million. Here's a look at Twitter's journey from humble beginnings to a company that has a valuation of about $18 billion. Twitter IPO: Executives ring the opening bell
GRAPHIC: Michelle Williams - The Washington Post.