The 4.2-m William Herschel Telescope (WHT) "The king of the mountain", Sky and Telescope, April 1997.

The William Herschel Telescope (WHT) is one of the the world's largest single-mirror telescope. Until 1993, when the American Keck I telescope was inaugurated, the WHT was considered the most powerful telescope in the world, because of its modern technology combined with the superb quality of the La Palma site. The WHT is the largest telescope in Western Europe.

Construction of the telescope building began in 1983. The telescope was shipped to La Palma in 1985 and first light was on 1st June 1987.

The WHT is financially supported by the British PPARC (Particle Physics and Astronomy Research Council) and the Dutch NWO (Nederlandse Organisatie voor Wetenschappelijk Onderzoek), in proportion of 80% and 20% respectively.

The WHT is operated on La Palma by the Isaac Newton Group of Telescopes (ING) which also operates the 2.5 m Isaac Newton Telescope (INT) and the 1 m Jacobus Kapteyn Telescope (JKT).

Astronomical time in WHT is distributed as follows: 60% for British astronomers, 15% for Dutch astronomers, 20% for Spanish astronomers and finally 5% is dedicated to large international projects.