The law of the sea, one of the oldest areas of international law, is now substantially codified in the 1982 United Nations Convention on the Law of the Sea (‘UNCLOS’), the ‘constitution for the oceans’. UNCLOS ushered in the modern law of the sea, providing a comprehensive regime for maritime zones, navigational rights and freedoms, fishing and other uses of the world’s oceans that cover approximately 70% of the Earth’s surface. As an island country with extensive maritime zones, Australia has a major stake in the law of the sea and has been actively involved in its development and implementation. Australia was one of the original signatories to UNCLOS and ratified it in 1994, the year it entered into force generally. The central issues of concern for the law of the sea have traditionally been the extent of maritime jurisdiction and navigational rights. However, a much broader range of matters is addressed in contemporary law and practice, from sustainable fisheries management through to mining of the deep seabed beyond national jurisdiction. There are also major new challenges on the horizon – none more so than climate change.