Class actions have been possible in the US for many years and are the main procedure by which large-scale commercial disputes involving large numbers of claimants are resolved. The requirements around them are well-established: a court must certify the class before the action may commence and they are generally run on an opt out basis. Both compensatory and punitive damages are obtainable, if sufficiently egregious conduct on the part of defendants can be established. Recent decisions by the US Supreme Court have increased the burden on putative class action plaintiffs but also reinforced the continued viability of the class action mechanism, and the number of class actions is likely to continue to increase.