The authors thank the Marketing Science Institute, the UCLA Price Center for Entrepreneurship and Innovation, and the Law & Economics Center Program on Economics & Privacy for generous funding. The authors thank Tobias Salz for early contributions to this project as well as Randy Bucklin, Sam Goldberg, Garrett Johnson, and Silvio Ravaioli for helpful comments. The authors thank audiences at the Cornell Johnson, Digital Economics Paris Seminar, Econometric Society Interdisciplinary Frontiers Economics and AI/ML Meeting, Google Economics, GMU Program on Economics & Privacy Empirical Research Workshop, IIOC, Marketing Strategy Meets Wall Street Conference, Platform Competition Workshop (USC), Toulouse Economics of Platforms Seminar, UC Boulder Leeds, and UCLA Anderson for helpful comments. The authors further thank Maurice Rahmey, Nils Wernerfelt and, Michael Zoorob for answering questions about advertising on Meta as well as Andrew D’Amico, Chelsea Mitchell, Sangwook Suh, and Kevin Wang for excellent research assistance. Furthermore, the authors thank Carol Doyle for help with procuring the Kantar Vivvix data set. All errors are the authors’ own. Authors are listed in alphabetical order. An earlier version of this paper was circulated as “Privacy Regulation and Targeted Advertising: Evidence from Apple’s App Tracking Transparency.”