Ocean plastics constitute a source of pollution and a threat to the marine environment and are thus subject to the general obligations to protect and preserve the marine environment in Part XII of the 1982 United Nations Convention on the Law of the Sea. This chapter will critically examine the scope and extent of these obligations, which impose a due diligence obligation to prevent, reduce, and control pollution of the marine environment. The law of the sea, through the London dumping regime and the 1973/78 MARPOL Convention establishes a robust set of obligations relating to the discharge of plastics at sea from vessels although implementation and compliance with these rules is not always effective. By contrast, the global regime for land-based plastic marine pollution is far from robust, comprising largely soft law instruments and initiatives, supported by extensive but normatively variable regional action plans and other measures. The new plastics treaty, consequently, has the potential to make a genuinely meaningful contribution to the ocean plastics regime complex and the ways in which this might occur are explored in the concluding part of this chapter.