Recent calls for using the antitrust laws to break up the large Internet giants are misplaced for a number of reasons. First, similar efforts against oil, tobacco, motion-picture, and telecommunications monopolies have not proved to be beneficial to economic welfare. Second, the failure to break up Microsoft using Section 2 has not proved to be a mistake: competition in operating systems and Internet browsers has flourished recently. Finally, a Section 2 case against Amazon, Facebook, or Google could not succeed if it focused on the digital advertising market. Even in a case based on market power on the other side of their platforms, a structural remedy—a break-up—would not improve economic welfare in the long run.