This book models the reaction of firms to Federal Trade Commission (FTC) decisions to seek to block proposed horizontal mergers. Finns' responses to the FTC are shown to depend on a number of factors, including the structural merits of the FTC challenge, the efficiencies potentially arising from the transaction, and the cost to the firms of fighting the FTC in court. For a large number of the FTC's merger challenges, we find that firms have strong incentives to settle with the Commission, regardless of the cases' competitive merits. Therefore, in these matters the Commission appears to have powers more like a regulatory agency than a prosecutor.