In 2002, the European Commission adopted a new Leniency Notice that sought to address certain of the shortcomings identified under the pre-existing Leniency Programme and achieve a substantial degree of convergence with the US Leniency Program. The 2002 Notice is widely considered to have led to a significant increase in the number of cartel infringement decisions. It has also transformed legal practice in this area, in particular by sensitising EU companies to the complex strategic considerations that shape the decision whether or not to seek leniency. Although papers and speeches delivered by Commission officials have improved understanding of the Commission's practice, several important procedural and practical issues remain unresolved. Among other things, there would be considerable benefits to formalising in a set of Guidelines important recent changes in the Commission's administrative practice in respect of leniency that are capable of having material legal effects. Further, the Modernisation Programme, which comes into force in May 2004, has created a pressing need for the Commission and national competition authorities to consider the potential implications of multiple proceedings at EU and national level, including where there is a risk of individual criminal sanctions for cartel behaviour under national law. This article suggests various ways in which these uncertainties might be resolved.