There is widespread dissatisfaction with existing antitrust enforcement. The European Union has enacted comprehensive legislation to address perceived antitrust limitations, and several proposals to amend US antitrust laws have followed its lead. Most of the actual and proposed laws target firms that dominate the digital economy, while others have measures to tighten antitrust enforcement more generally. Market power has increased in the United States and most advanced economies, but it has not been uniformly associated with higher prices or lower productivity. Nonetheless, antitrust reforms can benefit consumers and address concerns about the concentration and exercise of economic power. In the United States, legislation would be desirable to amend rulings that are excessively deferential to antitrust defendants. However, most enacted and proposed reforms include prohibitions or obligations that depart from traditional antitrust principles and create potential risks for consumer welfare. Expected final online publication date for the Annual Review of Economics, Volume 15 is August 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.