Ellen Siminoff (born Milwaukee, Wisconsin) is an entrepreneur and investor. Siminoff was a founding executive and Senior Vice President of Yahoo, where she ran business development, corporate development, and the small business and entertainment business units between 1996 and 2002.
Siminoff is currently Chief Executive Officer of Shmoop, an educational website. She was former Chairman and former CEO of Efficient Frontier. In her 4 years as CEO, Siminoff built Efficient Frontier into the largest buyer of search advertising keywords on Google  and one of the 25 most valuable privately held companies in Silicon Valley, at an estimated $275 million valuation, according to Silicon Alley Insider. Efficient Frontier was sold to Adobe for over $400M in 2012.
Siminoff sits on the board of directors for:
and previously in:
- "Yahoo! Directors & Officers". Yahoo. Archived from the original on 2013-03-19.
- "Management Team". Shmoop. Retrieved 2013-10-07.
- "Board Members". Efficient Frontier. Archived from the original on 2008-07-04.
- "Efficient Frontier: Hacking Madison Avenue". BusinessWeek. 2006-07-23. Retrieved 2013-10-07.
- "23. Efficient Frontier". Business Insider. 2008-03-28. Retrieved 2014-05-05.
- Hardy, Quentin (2005-09-05). "2005 E-Gang: The Keyword Keeper". Forbes.com. Retrieved 2013-10-07.
- Markoff, John (2007-05-05). "Rumors Fly on Microsoft and Yahoo". The New York Times.
- Helft, Miguel (2006-12-07). "Industry Insiders Praise Yahoo Choice for Key Post". The New York Times.
- Helft, Miguel (2008-04-03). "Google Cutting 300 Jobs at DoubleClick". The New York Times.
- Helft, Miguel (2007-02-05). "A Long-Delayed Ad System Has Yahoo Crossing Its Fingers". The New York Times.
- "Q&A with Efficient Frontier's Ellen Siminoff". iMediaConnection.com. Retrieved 2013-10-07.
- "Journal Communications, Inc. Elects Ellen Siminoff to Board of Directors" (Press release). Business Wire. February 14, 2007.
- Siminoff, Ellen F. "Ellen Siminoff: Executive Profile & Biography". BusinessWeek. Retrieved 2013-10-07.
- "Zynga Appoints Ellen Siminoff to Board of Directors". Zynga. 2012-07-19. Archived from the original on 2013-06-24.
- "Mozilla Jobs — Open Positions". Mozilla Corporation. Retrieved 2013-10-07.
- "Three Mozilla Board Members Resign over Choice of New CEO". Digits (The Wall Street Journal). Retrieved 204-03-28. Check date values in:
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