To combat cartels, competition authorities are increasingly applying leniency programs. This is intended to encourage companies to exit cartels. The European Commission has been using such a program since 1996, which was revised in 2002. The successful Leniency Notice of the US Department of Justice served as a model for this. The Federal Cartel Office has had a bonus program since 2000. This work presents the EU leniency programs and the related practices, discussing the fundamental and procedural legal issues involved. It examines to what extent the goal of effective cartel enforcement justifies a leniency program. The innovations resulting from the reform of EU cartel law for the application of the leniency program are addressed. Finally, the specifics of the German bonus program and the US Leniency Notice are highlighted.