Pollution from land based sources remains one of the most pressing threats to the health, resilience and services of the marine environment. The solutions are complex, demanding multilateral, collaborative and proactive policy responses, ranging from education and awareness campaigns, to financial and economic incentives, to legislative and regulatory regimes underscored by resolute punitive measures for environmental negligence and industrial laggards. Contemporary multilateral mechanisms for protecting the marine environment from land-based sources of pollution – whether hard or soft law – inevitably reflect the rights and principles found in the 1982 United Nations Convention on the Law of the Sea (LOSC). Part XII speaks of obligations, implying that states must deliberately and actively address various threats to the marine environment. Specifically, Article 207 requires states to adopt laws and regulations to prevent, reduce and control pollution of the marine environment from land-based sources. The chapter explores global and regional cooperation to address land-based sources of marine pollution, international environmental law of an indirect nature, and the growing labyrinth of soft law. The flexible nature of the 1995 Global Programme of Action for the Protection of the Marine Environment from Land-based Activities is reviewed, highlighting the need for adaptive national approaches that avoid regulatory paradoxes. Enforcement and compliance of domestic legislation, as well as the role of information is addressed, stressing the importance of sustained research and monitoring of the marine environment. The chapter questions whether the current fragmented system of international environmental law and governance is capable of solving the problem. It concludes that a rejuvenated effort by a complex and diverse network of landholders, government, industry, community groups and research organizations is urgently needed to give full effect to international marine environmental law and the obligation, enshrined in the LOSC, to protect the marine environment from land-based sources of pollution.