In 2010, the US Department of Justice and the European Commission approved the proposed agreement between Microsoft and Yahoo! to combine their Internet search and paid search advertising businesses. Compass Lexecon teams were retained by both Yahoo! and Microsoft to provide antitrust consulting services before the American and European regulators. Compass Lexecon conducted extensive analyses related to the potential competitive effects of the proposed agreement (including theoretical and empirical analyses of advertiser participation in search advertising auctions), conducted large scale and detailed data processing to comply with requests for information from regulators in the US and Europe, and assisted with the Form CO for submission to the European Commission. We worked with both US- and Europe-based counsel, including Michael Weiner and Alec Chang of Skadden, Arps, Slate, Meagher & Flom LLP, Simon Baxter now also at Skadden, and Frances Dethmers of Clifford Chance LLP for Yahoo!; and Rick Rule, Jonathan Kanter, and Joseph Bial of Cadwalader, Wickersham & Taft LLP and Jonas Koponen of Linklaters LLP for Microsoft. Compass Lexecon’s Yahoo! team included Robert Willig, Jon Orszag, Glenn Mitchell, Lacey Plache, Jay Ezrielev, Yair Eilat, YoungBae Moon, and other staff in Los Angeles, D.C., and San Francisco. Our Microsoft team included Dennis Carlton, Rick Flyer, Colleen Loughlin, Eugene Orlov, Todd Kendall, and a team in the Chicago office.