HM Prison Portland is a male Adult/Young Offenders Institution in the village of The Grove on the Isle of Portland, in Dorset, England. It is operated by His Majesty's Prison Service. The prison was originally opened in 1848 as an adult convict establishment, before becoming a Borstal in 1921, and a YOI in 1988. In 2011 it became an Adult/Young Offenders establishment.

The Isle of Portland is a tied island, 6 kilometres (4 mi) long by 2.7 kilometres (1.7 mi) wide, in the English Channel. The southern tip, Portland Bill, lies 8 kilometres (5 mi) south of the resort of Weymouth, forming the southernmost point of the county of Dorset, England. A barrier beach called Chesil Beach joins Portland with mainland England. The A354 road passes down the Portland end of the beach and then over the Fleet Lagoon by bridge to the mainland. The population of Portland is 13,417.