This chapter surveys the extensive work undertaken by the International Maritime Organization (IMO) to protect the marine environment. It argues that marine environment issues cannot be the exclusive responsibility of one international organization, even one as proactive as the IMO. The chapter offers a variety of suggestions that might be looked into to improve the effectiveness of IMO measures. It also notes that flag states do not always live up to their responsibilities under the UN Convention on the Law of the Sea (UNCLOS) with regard to the exercise of effective control and jurisdiction over ships flying their flags. In this light, Port State Memorandum of Understanding (MoU) reports frequently observe substantial deficiencies on a number of vessels, whether flagged under open registries or not. It remains to be seen whether the recently adopted IMO compulsory audit scheme may cast further light on these issues.