3. Marissa Mayer
40u40 main marissa mayer
Age: 37

President and CEO, Yahoo

The Google veteran (she was its 20th employee and first female engineer) received a call from Spencer Stuart ├╝ber-recruiter Jim Citrin in June, dangling the top job at Yahoo. The move was risky; Yahoo's notoriously fickle board has named four CEOs in five years. But after 13 years at Google, most recently steering its local and map business, Mayer jumped at the promotion, ) notwithstanding the expected October arrival of her first baby (a son, born Sept. 30). Mayer's product development chops -- Google's iconic search page design is said to be her brainchild -- provide hope for the struggling Yahoo, which needs serious help growing revenue -- and its stock price.

First move: Free lunch for everyone at Yahoo's Silicon Valley office.

--Colleen Leahey

  @FortuneMagazine - Last updated October 17 2012 05:11 PM ET
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The job creators

Organizations headed by some of these top young minds in business have grown this past year, many of them hiring at an impressive rate. Here are seven examples.

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