[Kristofer Erickson and Martin Kretschmer] Abstract: What factors lead a copyright owner to request removal of potentially infringing user-generated content? So-called “notice-and-takedown” measures are provided in the United States under Section 512 of the U.S. Copyright Act (as amended by the Digital Millennium Copyright Act 1998) and enabled in the European Union under the Directive on Electronic Commerce (2000/31/EC). While the combination of limiting liability (“safe harbor”) and notice-and-takedown procedures was originally conceived as a means of balancing innovation with the interests of rightholders, there has been limited empirical study regarding their effects. This research investigates, for the first time, the factors that motivate takedown of user-generated content by copyright owners.