Environmental harm is a diverse problem. It can arise in various forms, ranging from environmental disasters causing pollution, to environmental nuisances. Almost by definition environmental harm often affects many and may cause widespread damage, as a result of which it becomes mass environmental harm. Such harm is an inevitable by-product of modern living in today’s mass consumer society. This paper examines the phenomenon of mass environmental harm, its distinctictive features and the challenges that these present for litigation. These include issues surrounding toxic torts; causation and evidential complexity; latency; legal cost; and the corporate veil. It explores some novel remedies for mass environmental harm, such as interim measures and medical monitoring. It then explores routes to collective redress for mass environmental harm, where it examines the role of public law and regulation, private enforcement and other techniques such as Alternative Dispute Resolution. It also examines solutions that multi-party actions (MPAs) may offer as one form of collective redress for environmental mass harm. This is illustrated by the collective action experience of the EU and some of its individual member states and also of a number of common law jurisdictions, including Ireland, England and Wales and the United States. There is a detailed examination of Ireland as a case-study of a common law juridiction that does not have an effective MPA procedure and the difficulties that this presents. Finally, the paper speculates what may lie ahead for environmental mass harm redress given ongoing developments, for example at EU level and also in the area of human rights and the Aarhus Convention. The paper demonstrates that there is not a huge likelihood that MPAs will be brought for mass environmental harm and this is because of three reasons: firstly, the environment does not fit naturally within the framework that is traditionally recognised for the protection of private rights; secondly, it is predominantly public authorities that play the primary role in environmental enforecement in Europe; and thrirdly, there are many difficulties with private enforcement (these are discussed in detail). These problems support academic commentory that tort law in the past was not equipped to address the problems of modern pollution and torts. This would appear to undermine the potential role for MPAs in the environmental mass harm sector. It would appear that the best solution for mass environmental harm to have the widest range of possible legal remedies in order to deter pollution, to compensate harm and to protect the environment. While mass litigation is not necessarily the best solution to environmental mass harm claims, it would appear that it could benefit from the managerial advantages that MPAs can confer.