Earlier this year, Corporate Counsel contacted more than 300 law firms and asked them to provide us with a list of patent lawsuits they either filed on behalf of plaintiffs in federal district court in 2011 or were hired to defend against. To be considered for this survey, the cases in question had to be active as of the end of 2011. We did not count cases before the International Trade Commission or appellate courts. Some firms listed multiple district court cases with the same plaintiff. We did not rank firms that served as local counsel in the bulk of cases submitted. As such, some firms this year were excluded from our rankings. For example, Delaware-based Potter Anderson & Corroon would have ranked third overall, with 115 cases.