The legality of a horizontal merger under section 7 of the Clayton Act turns on a reckoning of its social costs and benefits. This paper reviews what economics has to say about that reckoning and explores the relationship between economic learning and merger law and policy

This chapter first reviews the economic theory underlying the unilateral competitive effects of mergers, focusing on the Cournot model, commonly applied to homogeneous products; the Bertrand model, commonly applied to differentiated consumer products; and models of auctions and bargaining,...

The downstream effects of mergers between manufacturers of differentiated consumer products are partly determined by the relationship between the merging manufacturers and retailers. That relationship may be such that the retail price effects of the merger are exactly those if the manufacturers...

Following merger, an optimal mechanism discriminates against merging bidders with higher reserve prices and by allocating more often towards non-merging bidders. In this setting, we show that mergers always harm the auctioneer, benefit non-merging bidders, can increase total surplus, and have...