The Cosmic Anisotropy Telescope (CAT) was a three-element interferometer for cosmic microwave background radiation (CMB/R) observations at 13 to 17 GHz, based at the Mullard Radio Astronomy Observatory. In 1995, it was the first instrument to measure small-scale structure in the cosmic microwave background. When the more sensitive Very Small Array came online in 2000, the CAT was decommissioned and partly dismantled.