The Hubble Space Telescope (HST) is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4-meter (7.9 ft) aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared.
Many Hubble observations have led to breakthroughs in astrophysics, such as accurately determining the rate of expansion of the universe.
The HST is one of the largest and most versatile space telescope and is well known as both a vital research tool and a public relations boon for astronomy. The HST was built by the United States space agency (NASA), with contributions from the European Space Agency (ESA).
Launched in 1990, scientists found that the main mirror had been ground incorrectly, compromising the telescope's capabilities. The telescope was restored to its intended quality by a servicing mission in 1993.
Hubble is the only telescope designed to be serviced in space by astronauts. The telescope is expected to function until at least 2014. Its scientific successor, the James Webb Space Telescope (JWST), is to be launched in 2018 or possibly later.
adapted from wikipedia
A gallery of HST can be found here.
A video to celebrate the 22nd anniversary of HST, enjoy it: