Private antitrust litigation, long the preserve of the US, is now also booming in Europe and elsewhere, and increasingly includes class actions or other forms of collective legal procedures. What are the greatest challenges for plaintiffs and defendants in multi-jurisdictional cases?  What has been the impact of EU Damages Directive and does harmonisation there need to go further? Does the success of private litigation mean that leniency policies need reform to restore incentives? What about monopolisation and dominance claims? How is damages quantification best done? Does the US experience have lessons for the rest of the world?