Wellington Harbour, officially called Wellington Harbour / Port Nicholson, is a large natural harbour on the southern tip of New Zealand's North Island. The harbour entrance is from Cook Strait. Central Wellington is located on parts of the western and southern sides of the harbour, and the suburban area of Lower Hutt is to the north and east.

Cook Strait separates the North and South Islands of New Zealand. The strait connects the Tasman Sea on the northwest with the South Pacific Ocean on the southeast. It is 22 kilometres (14 mi) wide at its narrowest point, and is considered one of the most dangerous and unpredictable waters in the world. Regular ferry services run across the strait between Picton in the Marlborough Sounds and Wellington.