Calf of Man (Manx: yn Cholloo) is a 250 hectare island (almost 1 square mile), off the southwest coast of the Isle of Man. It is separated from the Isle of Man by a narrow stretch of water called the Calf Sound. Like the nearby rocky islets of Chicken Rock and Kitterland, it is part of the parish of Rushen. It has two seasonal inhabitants. The word 'calf' derives from the Old Norse word kalfr which means a small island lying near a larger one. It is possible to reach the Calf of Man by boat from both Port Erin and Port St Mary. Cow Harbour and South Harbour are the main landing places.
Until 1939 the island was under private ownership by the Keig family, but in that year the island was donated to the National Trust to become a bird sanctuary. In 1951 the Manx National Trust was established, which became Manx National Heritage. The island has been a bird observatory since 1962 and welcomes visits from volunteers and ornithologists. The observatory is able to accommodate up to eight visitors in basic self-catering accommodation which can be booked through Manx National Heritage.
The Calf of Man currently boasts the world's highest density of lighthouses: two lighthouses were built in 1818 by Robert Stevenson to warn mariners of the hazards of the Chicken Rocks off the south end of the Calf. These were replaced in 1875 by a lighthouse built on the Chicken Rocks themselves. In 1968, a third lighthouse was built on the Calf after a severe fire destroyed the Chicken Rocks light. The Chicken Rocks lighthouse was later rebuilt.
In 2006 Manx National Heritage employed the charity Manx Wildlife Trust as the Calf Warden Service Provider, but it retains ownership.
Between the Isle of Man and the Calf is the islet of Kitterland, while the islets of Yn Burroo and The Stack lie close to the Calf's shore. Almost a mile southwest of the Calf is Chicken Rock, the most southerly part of the Isle of Man's territory.
Calf of Man is home to a breeding population of Manx Shearwaters, a seabird which derives its name from its presence in Manx waters.