The Isle of Portland is a large limestone island in the English Channel. It is near Weymouth in Dorset. The island is connected to the mainland by a large pebble tombolo called Chesil Beach, and by the A354 road bridge to Weymouth.

The island makes up part of the Jurassic Coast World Heritage Site.

The island is home to two small towns, Fortuneswell and Easton.

The island, and its large harbour was home to much of the Royal Navy during World War II, and because of this the island was heavily bombed. The naval base has now gone. The island is still home to HMP Portland and HMYOI Portland, and the harbour contains Britain's only prison ship.

The southern tip of the island, known as Portland Bill, is home to a lighthouse.

Large areas of London were built from Portland Stone, and nearby Purbeck limestone, after the Great Fire of London and bombing in world war II, and the island is covered in the remains of quarries..