Founded in 2002, Keystone Strategy debuts in the GCR 100 this year as its focus–competition in the technology sector – has become a preoccupation of enforcers around the world. Somewhat unusually for this survey, Keystone is not a pure economics consultancy. It offers an array of expertise to both tech companies and their competition critics. Today, it counts four of the largest such companies – Facebook, Amazon, Apple and Microsoft – as important clients. It also continues to advise antitrust enforcers from its offices in the US, UK, France, Italy, Brussels, Germany and Australia, though most of this work remains confidential for now. Who's Who Legal: Competition nominee Susan Athey is a highly influential platform and data economist, while fellow nominee Ernst Berndt specializes in innovation economics. In the past year, the team has added Ara Stepanyan from the International Monetary Fund, and Assaf Zimring from Cornerstone. Athey testified about merger efficiencies on behalf of the DOJ in the agency's challenge to the AT&T/Time Warner merger, analyzing the companies' plans to create an online advertising platform using first-party data from its subscribers. She and fellow Keystone expert Robin Lee both spoke at one of the US Federal Trade Commission's hearings on competition and consumer protection in the 21st century. Athey, assisted by Marowits and others, again testified for the government as the FTC successfully sued 1-800 Contacts for preventing rival contact lens sellers from buying search advertisements where the search terms included the company's trademarks. Keystone is also providing analysis of the anticompetitive effects of this restraint in the follow-on litigation, and in similar private lawsuits against hotel chains that allegedly had similar agreements not to compete in search ads. Marco Iansiti is providing expertise for a confidential third party in the European Commission's Android and AdSense cases against Google. In another private litigation, Athey and Marc Rysman worked on behalf of CollegeNet's claim that Common Application abused its dominance in the college application market by requiring exclusivity arrangements that excluded competition for high-quality application systems. Keystone analysed market definition, innovation and competition impacts; the case settled in February 2019, with Common Application agreeing to change certain practices. View the full ranking here.