Revenue: Not available
Headquarters: San Francisco
Industry: Online reviews
Founded: 2005
Employees: 750

When it launched six years ago, Yelp was a site where San Francisco hipsters posted attitude-laden reviews of bars and restaurants. Today it operates 63 city sites in nine countries and attracts more than 53 million unique monthly visitors. Yelpers, as the company's myriad unpaid reviewers proudly call themselves, opine on everything from churches to plumbers to dog groomers. The network recently published its 20-millionth review, a write-up of an L.A. eatery called Joan's on Third. (The reviewer described it as "Auntie Em's kitchen on steroids.") Yelp has raised $56 million in angel and VC funding and is not currently profitable. It has attracted its share of controversy, including allegations that it has suppressed negative reviews to please its advertisers. Yelp founder and CEO Jeremy Stoppelman (right) dismisses the complaint, preferring to look ahead: "We'll be the 3,000-pound gorilla in this space. Nobody else generates our depth of content."

--Richard McGill Murphy

Last updated August 03 2011: 6:22 PM ET
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