18 years of science with the Hubble Space Telescope.

After several decades of planning, the Hubble Space Telescope (HST) was launched in 1990 as the first of NASA's Great Observatories. After a rocky start arising from an error in the fabrication of its main mirror, it went on to change forever many fields of astronomy, and to capture the public's imagination with its images. An ongoing programme of servicing missions has kept the telescope on the cutting edge of astronomical research. Here I review the advances made possible by the HST over the past 18 years.