Leniency has emerged as one of the main enforcement instruments used by competition authorities to combat cartels. Offering immunity from punishment is believed to destabilise already existing cartels and deter undertakings from entering into such arrangements. This book offers the first in-depth analysis of the scope of leniency in European Union (EU) competition law, considering three crucial ramifications – ensuring a leniency applicant can self-report with confidence, retaining the right to compensation of those who have suffered losses due to the cartel and furthering the objective of undistorted competition within the internal market. With thorough insight into the interaction between the Commission’s Leniency Notice and public and private enforcement, the author fully explains such aspects of the subject as the following: who is eligible for leniency; liability of an immunity recipient; the EU fining system; disclosure of leniency evidence; scope of public authorities reaching out to cartel infringers; the immunity recipient and follow-on damages claimants; the immunity recipient and subsequent leniency applicants; effect of the Damages Directive; and the European Economic Area dimension. The author offers cogent suggestions about how the shortcomings of the Commission’s leniency offer can be ameliorated and which regulatory steps should be taken to give the policy greater leverage. The author calls for increased harmonisation at national level in the EU and compares leniency practice in US antitrust law. As a comprehensive analysis of the practical application of current policy and procedure in EU cartel enforcement, the book clearly shows the ways in which the scope of leniency is manifest in the interaction between public and private enforcement, evaluating which interaction is most effective. Its practical character will be recognised and welcomed by competition law practitioners and policymakers, who will strengthen their grasp of leniency procedure and clearly discern implications for competition infringement cases.