After thirty years, the debate over antitrust's ideology has quieted. Most now agree that the protection of consumer welfare should be the only goal of antitrust laws. Execution, however, is another matter. The rules of antitrust remain unfocused, insufficiently precise, and excessively complex. The problem of poorly designed rules is severe, because in the short run rules weigh much more heavily than principles. At bottom, antitrust is a defensible enterprise only if it can make the microeconomy work better, after accounting for the considerable costs of operating the system.