The Tasman Sea is the large body of water between Australia and New Zealand and is a south-western segment of the South Pacific Ocean. The sea was named after the Dutch explorer Abel Janszoon Tasman, discoverer of New Zealand and Tasmania. The British explorer Captain James Cook later extensively explored the Tasman Sea in the 1770s as part of his first voyage of discovery.

The Tasman Sea is deemed by the International Hydrographic Organisation to include the waters to the east of the Australian states New South Wales, Victoria and Tasmania. The northern state of Queensland neighbours the Coral Sea, and the boundary between New South Wales and Queensland is also used as the boundary between the two seas.

The Tasman Sea features a number of mid-sea island groups, quite apart from coastal islands located near the Australian and New Zealand mainlands:

• Lord Howe Island and its subsidiary islands
• Ball's Pyramid
• Norfolk Island, in the extreme north of the Tasman Sea, on the border with the Coral Sea

These island groups are each Australian possessions.