Sidley Austin LLP, formerly known as Sidley Austin Brown & Wood LLP, is one of the oldest law firms in the world. It is the sixth-largest U.S.-based corporate law firm with over 1,600 lawyers, annual revenues of more than one billion dollars, and offices in 17 cities worldwide, with the most recent addition of Palo Alto, California in December 2009. It is a full-service law firm, with broad experience in transaction and litigation matters. Its original predecessor firm was founded in 1866 and had former first lady Mary Todd Lincoln, then the widow of PresidentAbraham Lincoln, among its earliest clients. The firm was formed as the result of the merger of two firms: the Chicago-based Sidley & Austin, founded in 1866, and the New York-based Brown & Wood, founded in 1914. The merger was completed in May 2001. The firm's headquarters is at One South Dearborn in the Chicago Loop, Chicago.
As of 2006, it was the 9th largest law firm in the world (and 5th in the US) by revenue. In September 2010, it received the most First-Tier National Rankings in the inaugural Best Law Firms Survey by US News and World Report.