Merger analysis has generally developed with a focus on mergers among sellers and whether a merger will create or enhance seller market power. The issue of buyer power, however, can be important in many merger cases. First, some mergers will combine two significant purchasers of a product or service. In such cases, the competitive analysis of the merger for those products or services assesses (1) whether the merger creates or enhances buyer power sufficiently to raise competitive concerns, and (2) whether competitive concerns are offset due to efficiencies resulting from the combination. Second, some seller mergers involve markets where customers have some level of buyer power. In such cases, part of the competitive assessment of the merger may be to determine whether the presence of buyer power will constrain the potential exercise of seller market power following the proposed merger. This chapter addresses both issues.