Masterton is the largest town (and local government district) in the Wairarapa region in the southeastern North Island of New Zealand. It is 85 kilometres northeast of Wellington and 70 kilometres south of Palmerston North, and stands on the banks of the Ruamahanga River.

Masterton is a thriving community with a population (2001) of 19,497. It therefore did not quite qualify to be a city by 1989 when the minimum requirement for that name was lifted from 20,000 to 50,000. A commuter rail link allows many residents easy access to work in the cities of Wellington, Lower Hutt, or Upper Hutt.

Named after pioneer Joseph Master, it was first settled by Europeans on 21 May 1854. It gained borough status in 1877.

Local industries involve service industries for the surrounding farming community. The town is the headquarters of the annual Golden Shears sheep-shearing competition.

Some residents of Wellington see Masterton as backward and inconsequential, and sometimes rather unkindly refer to it as masturbation over the hill.