The UN Convention on the Law of the Sea (LOSC), which was adopted in 1982, devotes a significant proportion of its provisions to the protection of the marine environment. This chapter seeks to assess the value of those provisions at the present time, more than 30 years after the adoption of the LOSC. The chapter does this in two distinct ways. First, it asks how the LOSC compares with an ideal general treaty for the protection of the marine environment that might be drawn up today. Second, the chapter tries to determine the impact and influence that the marine environmental provisions of the LOSC have had on the practice of States and international organizations. To these ends the chapter looks in turn at each of those matters with which, it is suggested, an ideal contemporary general marine environmental treaty would deal. Those matters are: principles for marine environmental policy-making and legislation; the conservation of species; the protection of habitats; the prevention of marine pollution; and climate change. The chapter considers how, if at all, the LOSC addresses each of those issues; and insofar as the LOSC does address them, the chapter comments on the adequacy and practical impact of the LOSC provisions in question. The chapter concludes that the LOSC has serious deficiencies, especially when compared with an ideal contemporary marine environmental treaty, most notably weaknesses in its substantive norms and its failure to provide adequately for its normative development. The most significant contribution of the LOSC has been to establish a clear jurisdictional framework for the adoption and enforcement of national measures to protect the marine environment.