Twitter Is Going Public. Here's How It Makes Money

Analysts valued Twitter at $10 billion earlier this year, and it may be worth a little more than that today. But as my colleague Matt Yglesias points out, the fact that it is filing confidentially implies that its annual revenues have not yet reached $1 billion. Following the lead of Facebook and other Internet companies whose fortunes depend on an enormous user base, Twitter has been cautious about turning its service into a money-maker so far, with ads few and far between on the site. So how does it make money, and why might it be worth so much?