The Hale Telescope is the largest telescope at the Palomar Observatory. The 200-inch (5-m) telescope is named after George Ellery Hale (1868-1938). Hale supervised the building of the telescopes at the Mount Wilson Observatory with grants from the Carnegie Institution of Washington: the 60-inch telescope in 1908 and the 100-inch telescope in 1917. These telescopes were very successful, leading to the rapid advance in understanding of the scale of the Universe through the 1920s, and demonstrating to visionaries like Hale the need for even larger collectors.

In 1928 Hale secured a grant of US$6 million from the Rockefeller Foundation for "the construction of an observatory, including a 200-inch reflecting telescope" to be administered by the California Institute of Technology (Caltech), of which Hale was a founding member. In the early 1930s, Hale selected a site at 5600 feet on Palomar Mountain in San Diego County, California, USA as the best site, and less likely to be affected by the growing light pollution problem in urban centers like Los Angeles. Corning Glass Works were tasked with making a 200-inch mirror out of a new glass blend called Pyrex. Construction of the observatory facilities and dome started in 1936, but because of interruptions caused by World War II, the telescope was not completed until 1948.

The Hale 200-inch remained the largest operating telescope in the world until the advent of the Keck telescopes in 1992 and 1996. It continues to be used every clear night for scientific research by astronomers from Caltech and their operating partners, Cornell University and the Jet Propulsion Laboratory. It is equipped with modern optical and infrared array imagers, spectrographs, and an adaptive optics system.