Auckland Island (Māori: Mauka Huka) is the main island of the eponymous uninhabited archipelago in the South Pacific Ocean. It is part of the New Zealand subantarctic area. It is inscribed in the UNESCO World Heritage list together with the other New Zealand Subantarctic Islands in the region.

The island has a land area of about 442.5 km² (170.9 sq mi), and is 42 kilometres (26 mi) long. It was formed 25 to 10 million years ago from a huge volcanic pile which formed two domes – one centred around Carnley Harbour in the south and another (the Ross Dome) around Disappointment Island to the west. The island is made of volcanic scoria, blanketed in over 2m of peat. It is notable for its steep cliffs and rugged terrain, which rises to over 600 m (1,969 ft). Prominent peaks include Cavern Peak, at 659 m or 2,162 ft; Mount Raynal, at 635 m or 2,083 ft; Mount D'Urville, at 630 m or 2,067 ft; Mount Easton, at 610 m or 2,001 ft; and the Tower of Babel, at 550 m or 1,804 ft.

The southern end of the island broadens to a width of 26 kilometres (16 mi), encompassing Carnley Harbour. At the western side a very narrow channel known as Victoria Passage separates the main island from the smaller Adams Island. Adams Island and the southern part of the main island form the crater rim; three kilometres (1.9 mi) north of Carnley Harbour's mouth lies Cape Lovitt, the westernmost point of New Zealand.^{[citation needed]}

There are distinct vegetation zones. There is a band of Southern rātā Metrosideros umbellata around the coast apart from on the western side, the height of which is determined by the shelter, aspect and degree of the slope. The rātā forest may extend into the Chionochloa tussock grasslands but in most places merges into a thick band of low, tight scrub dominated by Dracophyllum longifolium, Ozothamnus vauvilliersii and Myrsine divaricata. This scrub band is almost impenetrable and in places is dense enough to walk on top of.

An expedition report from 1907 describes the scrub thusly:

The subalpine scrub at 400 ft. made our advance extremely toilsome, the thick masses of Suttonia divaricata scrub had to be cut through before any progress could be made. Throughout our stay on the island this scrub was one of the worst drawbacks we had to encounter; from four to six feet high it is quite impassable with reasonable exertion; walking on the top can be undertaken only by a very light man. Only with the severest exertion can it be pushed aside to enable a man to pass, crawling under it is out of the question.

The scrub band breaks into patches and transitions into extensive grassland of Chionochloa antarctica which in turn merges into a sparsely vegetated fellfield community on the most exposed alpine areas. The megaherbs Anisotome antipoda, Anisotome latifolia, Bulbinella rossii, Pleurophyllum criniferum, Pleurophyllum hookeri, Pleurophyllum speciosum and Stilbocarpa polaris were historically found from the coast into the alpine, however the distribution and populations of these species have been severely impacted by the actions of introduced pigs.

Port Ross at the north end of Auckland Island is the only breeding site for the New Zealand population of southern right whales. Up to 400 may be found in the harbour during the winter months, and are regularly surveyed by the University of Otago.