Skokholm (Welsh: Ynys Sgogwm) or Skokholm Island is an island 2.5 miles (4.0 km) off the coast of Pembrokeshire, Wales, south of the neighbouring island of Skomer. The surrounding waters are a marine reserve and all are part of the Pembrokeshire Coast National Park. Both islands are listed as Sites of Special Scientific Interest.

Skokholm is 1 mile (1.6 km) long and 0.5 miles (0.80 km) wide, covering 106 ha (260 acres). Made up of Old Red Sandstone, its cliffs stand between 70 feet (21 m) in the northeast, to 160 feet (49 m) in the southwest. Battered by storms, the high cliffs and isolated nature of the island make it a haven for seabirds. There is a rock outcrop close to the centre of the island, which provides shelter to the island's only structures. Its greatest height is 55 metres (180 feet).

Whilst no trees grow on the island in modern times, Skokholm is possibly Norse for "wooded island", a combination of skógr (wood, modern Norwegian: skog) and holmr (small island, middle English holm and modern Scandinavian holme), named by the Vikings.

A published map from 1578 called Penbrok comitat by Christopher Saxton names the island as Sealine insul, and Angliae regni florentissimi nova descriptio, written by Matthias Quad and published in 1600, mentions the name of the island as Selome. Saxton also noted the small rocky island north of the main island as being 'Yardlan stone' (perhaps a corruption of the Welsh words Yr Llan ("the church") or perhaps Yr Llanw ("the tide").

The island is likely to have been settled for several thousand years; evidence of stone-age occupation has been found.

There is an undated charter in the British Museum by which William Marshal the Younger, Earl of Pembroke 1219–31, grants to a certain Gilbert de Vale, land in Ireland in exchange for lands in Pembrokeshire, including the island of 'Scogholm'. The revenue from the island from 1324 to 1472 was recorded in Ministerial Accounts. Some years later, the island was in the hands of Sir John Perrott, supposedly a natural son of Henry VIII. It appears (in Latin) on a 1578 map of Pembrokeshire as Skokeholme Insul.

The island was bought for £300 in 1646 by William Philipps, a barrister, and it was kept in the family for the next 360 years. In 2005 his descendant Mrs. Osra Lloyd-Philipps (1920 - 24 March 2005) of Dale Castle died. The trustees of the estate decided to offer the island for sale, with first refusal going to the Wildlife Trust of South and West Wales, who had managed the island for the last 50 years on their behalf. After a large fundraising effort, the island was successfully purchased in April 2006 for £650,000, and designated a national nature reserve in December 2008.

In 1933, Skokholm started functioning as a bird observatory, the first in Britain, founded by Ronald Lockley; its prime function was the ringing of wild birds of resident, visiting or migrating species and research. Lockley started the Pembrokeshire Bird Protection Society in 1938, now incorporated in the Wildlife Trust of South and West Wales. In 1948 the West Wales Field Society (WWFC), also now Wildlife Trust of South and West Wales, first took the Lease of Skokholm from the owners of the Dale Castle Estate. The WWFC followed on the Lease by Ronald Lockley which had run from 1927 but direct involvement commenced two years earlier when in 1946 the bird observatory was re-opened after the war. Ringing on Skokholm ceased from 1976. During the period of radar studies of migration around 1960 it became clear that bird movements as observed at the observatories were by no means representative of the whole and, inevitably, the significance of the observatories in the study of migration waned. Skokholm had been the site of the most thorough British studies of the European storm petrel and razorbill amongst the seabirds and the Eurasian oystercatcher and the northern wheatear amongst the landbirds. "There can be few other islands anywhere in the world that can boast the continuity of biological recordings, save for wartime years, that has taken place on Skokholm." John Fursdon, Warden 1946. Skokholm Island was re-accredited as a bird observatory in 2014, with resident wardens Richard Brown and Giselle Eagle.