The proliferation of class action regimes around the world has created significant risks for defendants who increasingly face parallel mass litigation or class action suits in a growing number of jurisdictions. How are these regimes developing in an antitrust context - are they opt in or opt out? What approach are the courts taking in terms of evidence and disclosure? Which regimes seem to be ”claimant friendly”. For parties and legal practitioners involved in cross-border class actions, how can an effective antitrust class action strategy be developed to handle concurrent lawsuits in different jurisdictions? What insights can be gained to preserve the defense of a case in one jurisdiction without compromising positions in others?