This chapter begins with an explanation of the various threats facing, first, marine biodiversity and, second, biodiversity in forests. Both suffer from numerous threats and from the increased cumulative impact of these threats. The chapter then considers the legal framework for governance of marine biodiversity, explaining that there have been four major documents or instruments which have driven this legal development more than have any others: Huig de Groot’s pamphlet Mare Liberum, published in 1609; the judgment in 1898 of the arbitral tribunal in the Bering Sea Fur Seals Arbitration; the Proclamation by US President Truman in 1945 of a ‘Policy with Respect to Coastal Fisheries in Certain Areas of the High Seas’; and finally the United Nations Convention on the Law of the Sea (UNCLOS) (adopted 1982, entered into force 1994). A fifth may soon be adopted – if current efforts toward a global convention on the protection of biodiversity in areas beyond national jurisdiction are successful. In addition to these, there are hundreds of relevant international instruments, of global, regional and bilateral scope. In contrast, it is explained, there is little international regulation of forests, with many of the most relevant instruments being of a non-binding nature, such as the Forest Principles of 1992. In the face of this absence of regulatory instruments, recourse must be had to instruments of a more general nature. In conclusion, similarities and differences are highlighted between the regulatory regimes for forests and the marine environment, and it is noted that while one is arguably over-, and the other under-, regulated, neither is having the desired effect, and biodiversity is declining in both. That neither approach is working effectively is instructive, and a topic worth further study.