The Cerro Tololo Inter-American Observatory (CTIO) is a complex of astronomical telescopes and instruments located at 30.169 S, 70.804 W, approximately 80 km to the East of La Serena, Chile, at an altitude of 2200 meters.  CTIO headquarters are located in La Serena, Chile, about 300 miles north of Santiago.

The CTIO complex is part of the U.S. National Optical Astronomy Observatory (NOAO), along with the Kitt Peak National Observatory (KPNO) in Tucson, Arizona.  NOAO is operated by the Association of Universities for Research in Astronomy (AURA) under cooperative agreement with the National Science Foundation (NSF).  CTIO, as part of the AURA Observatory in Chile, operates in Chile under Chilean law, through an Agreement with the University of Chile and with the auspices of the Ministry of Foreign Affairs of Chile.

The principal telescopes on site are the 4-m Victor M. Blanco Telescope and the 4.1-m Southern Astrophysical Research (SOAR) telescope.  One of the two 8-m telescopes comprising the Gemini Observatory is co-located with CTIO on AURA property in Chile, together with more than 10 other telescopes and astronomical projects.