There's never been a Web site like Facebook: more than 350 million people have accounts, and if the growth rate continues, by 2013 every Internet user worldwide will have his or her own page. And no one's had more access to the inner workings of the phenomenon than Kirkpatrick, a senior tech writer at Fortune magazine. Written with the full cooperation of founder Mark Zuckerberg, the book follows the company from its genesis in a Harvard dorm room through its successes over Friendster and MySpace, the expansion of the user base, and Zuckerberg's refusal to sell. The author is at his best discussing the social implications of the site, from the changing notions of privacy to why and how people use Facebook—increasingly it's to come together around a common interest or cause (the eponymous Facebook Effect). Though significantly more informative, thoughtful, and credible than Ben Mezrich's The Accidental Billionaires, it may be hamstrung by its late entry; the furor over Facebook has more or less subsided, and potential readers are more likely to be using the site than to be reading about its origins.