Mount Graham International Observatory (MGIO) is a division of Steward Observatory, the research arm for the Department of Astronomy at the University of Arizona, in the United States. It is located in southeastern Arizona's Pinaleño Mountains near Mount Graham. During development, it was first called the Columbus Project.
Construction of MGIO began in 1989. MGIO operates and maintains facilities for three scientific organizations. The first two telescopes, the Vatican Advanced Technology Telescope and the Heinrich Hertz Submillimeter Telescope began operation in 1993. The Large Binocular Telescope, one of the world's largest and most powerful optical telescopes, began operations using its mirrors independently in 2004, with joint operations between the two mirrors beginning in 2008.