Market definition under attack: how relevant is the relevant market?

Market definition is typically a central topic in every antitrust investigation, whether a proposed or consummated merger is challenged, or incases of monopoly and alleged abuse by a dominant firm. Courts regularly utilize the market definition methodology because the delineation of the relevant antitrust market determines the market shares of the participating firms, and the impact of the proposed transaction on competition. For decades now, a cross-jurisdictional consensus has existed, that market definition should be the focal point of any competition-related inquiry. Not withstanding, the 'more economic approach' governing contemporary competition law thinking, and the increasing affiliation to quantitative measures in the interpretation of antitrust concepts, threaten to undermine this hegemony. Along these lines, the New Horizontal Merger Guidelines (hereinafter: 'the New Guidelines'), promulgated by the US Department of Justice and the Federal Trade Commission in August 2010, represent a somewhat less unequivocal stance regarding the market definition process. Whereas the former 1997 Guidelines strictly adhere to a structural framework, of which market definition comprised the first step, the New Guidelines are more sceptical of its role and scope.