The Atacama Cosmology Telescope (ACT) is a custom-designed 6-meter microwave telescope employing superconducting bolometer array detectors, which will be located in the Atacama Desert of the Chilean Andes in 2006. It will provide maps of the cosmic microwave background at arcminute resolution and micro-Kelvin sensitivity over a hundred square degrees of sky. I will review the scientific motivation for building this instrument, explain some of the technologies which are necessary, and discuss plans for complementary astronomical observations. We aim to compile a catalog of 1000 galaxy clusters and redshifts, selected by their distortions of the microwave background. ACT will provide insights into a wide range of topics including the primordial spectrum of density fluctuations, the growth of structure in the Universe, and the evolution of galaxies. ACT is a collaboration between Princeton, Penn, Rutgers, Goddard Space Flight Center, NIST, and a number of other partner institutions.