The Kaipara Harbour is an inlet of the Tasman Sea located near the base of the North Auckland Peninsula on the western side of the North Island of New Zealand.

The harbour is one of the largest in the world. It is a very broad shallow harbour covering an area of 530 square kilometres and has more than 3200 km of shoreline. It extends for some 60 kilometres from north to south, and has a four kilometre wide entrance to the Tasman Sea halfway along its length. The Wairoa River has its outflow into the northern end of the harbour. Several large arms extend into the interior of the peninsula at the northeast of the harbour, one of them ending near the town of Maungaturoto, only ten kilometres from the Pacific Ocean coast.

Although officially called a harbour, the Kaipara is rarely used for shipping, owing to the treacherous tides and bars at its mouth. For this reason, no large settlements lie close to its shores, although many small communities lie along its coastline.

Administratively, the lower part of the harbour lies within the Auckland Region, while the upper half is within the Northland Region.