The Waikato (/ˈwaɪkɑːtɔː/) is a region of the upper North Island of New Zealand. It covers the Waikato District, Waipā District, Matamata-Piako District, South Waikato District and Hamilton City, as well as Hauraki, Coromandel Peninsula, the northern King Country, much of the Taupō District, and parts of the Rotorua Lakes District. It is governed by the Waikato Regional Council.

The Waikato stretches from Coromandel Peninsula in the north, to the north-eastern slopes of Mount Ruapehu in the south, and spans the North Island from the west coast, through the Waikato and Hauraki to Coromandel Peninsula on the east coast. Broadly, the extent of the region is the Waikato River catchment. Other major catchments are those of the Waihou, Piako, Awakino and Mōkau rivers. The region is bounded by Auckland on the north, Bay of Plenty on the east, Hawke's Bay on the south-east, and Manawatū-Whanganui and Taranaki on the south. Waikato Region is the fourth largest region in the country in area and population: It has a land area of 23,901.09 km² (9,228.26 sq mi) and a population of 532,100 (June 2025).

The region encompasses all or part of eleven territorial authorities, the most of any region of New Zealand. It is centred on the Waikato which consists of Waikato District, Matamata-Piako District, Waipā District, South Waikato District and Hamilton City. In descending order of land area the eleven territorial authorities are Taupō District (part), Waikato District, Waitomo District (part), Thames-Coromandel District, Ōtorohanga District, South Waikato District, Matamata-Piako District, Waipā District, Hauraki District, Rotorua Lakes District (part), and Hamilton City.

The name for the region is taken from the Waikato River; waikato is a Māori word traditionally translated as "flowing water" (specifically, wai = "water" and kato = "the pull of the river current in the sea").

When Waikato is used in spoken language some people use it in the definite article, "the Waikato", whereas some people do not use "the". It is unknown why a difference is made. "The" usually refers to a smaller region than the Waikato local government region. Two definitions that would meet with wide acceptance are those of the Waikato rugby football union and of Hamilton Waikato tourism.^{[citation needed]}

To the west, the region is bounded by the Tasman Sea. The coastal region is largely rough hill country, known locally as the Hakarimata Range, though it is more gently undulating in the north, closer to the mouth of the Waikato River. The coast is punctured by three large natural harbours: Raglan Harbour, Aotea Harbour, and Kāwhia Harbour. The area around Raglan is noted for its volcanic black sand beaches and for its fine surfing conditions at Manu Bay and Ruapuke beach.

To the east of the coastal hills lies the broad alluvial plain of the Waikato River. This region has a wet temperate climate, and the land is largely pastoral farmland created by European settlers draining the extensive natural swamps, although it also contains undrained peat swamp such as the 200 km² (77 sq mi) peat dome south of Ngatea. It is in the broad undulating Waikato Plains that most of the region's population resides, and the land is intensively farmed with both livestock, mainly dairy cattle but with sheep farming on the hillier west margins, and crops such as maize. The area around Cambridge has many thoroughbred stables.

The north of the region around Te Kauwhata produces some of New Zealand's best wines. Dozens of small shallow lakes lie in this area, the largest of which is Lake Waikare.