Although the concept of leniency programmes has been universally accepted, there is no consensus on the required details of the individual policies. Some have proven a great success, whilst others have produced fewer results. Although there are clearly difficulties in determining the effectiveness of a leniency programme in practice, this chapter nonetheless aims to draw out some lessons on the common features of successful leniency programmes from the theoretical and practical viewpoints. To achieve this aim, the chapter comprises five substantive sections in addition to its conclusion. Section II outlines the global trend towards the adoption of antitrust leniency programmes. Section III explains very briefly the economics that underlie the employment of such leniency programmes. Section IV focuses on the experience of the early adopters of leniency programmes and identifies from that experience the internal and external factors that can impact upon success in this context. Section V outlines the challenges that leniency programmes present for ‘younger’ competition authorities. Drawing upon the analyses from earlier sections, Section VI proceeds to outline six criteria for the successful implementation of leniency programmes. Finally, Section VII concludes the chapter.