Recent merger cases in KFTC and courts have applied advanced methodologies in defining relevant markets. Critical loss analysis became a standard methodology to define both product and geographic markets. Concerning product markets, special types of markets, such as cluster markets, open markets and two-sided markets, were identified and analyzed. Concerning geographic markets, KFTC applied Elzinga-Hogarty Test and "a union of overlapping circles" approach. Meanwhile, US Horizontal Merger Guidelines were amended in 2010 to introduce new methodologies to directly estimate the anti-competitive effect of mergers, before the agencies define markets. Critics maintained that the Guidelines marginalize market definition and thereby conflict with precedents, and UPP, one of the new methodologies, is not capable of providing practical and reliable guidelines to business community. However, the Guidelines does not abolish market definition, but allow more flexibility to the agencies` choice of methodologies to analyze mergers according to the specifics of each case. Thus the amendment is an evolution rather than a revolution, to which courts could adapt themselves in the near future. In Korea, the decisions and guidelines of the KFTC already reflect a part of the development toward the reduced role of market definition in merger review, and a court decision partially endorsed a decision by the KFTC in that direction. Thus we could expect the introduction of more state-of-the-art methodologies for merger analysis that could directly assess competitive effect of a merger.