The Cerro Tololo Inter-American Observatory (CTIO) is an astronomical observatory located on Cerro Tololo in the Atacama Desert of northern Chile, with additional facilities located on Cerro Pachón about to the southeast. It is within the Coquimbo Region and approximately east of La Serena, where support facilities are located. The site was identified by a team of scientists from the Chile and America in 1959, and it was selected in 1962. Construction began in 1963 and regular astronomical observations commenced in 1965. Construction of large buildings on Cerro Tololo ended with the completion of the Victor M. Blanco Telescope in 1974, but smaller facilities have been built since then. Cerro Pachón is still under development, with two large telescopes inaugurated since 2000, and one in the early stages of construction.

Le Cerro Tololo Inter-American Observatory (ou CTIO, ) est un observatoire astronomique américain situé dans la vallée de Elqui, sur le Cerro Tololo, au Chili. L'observatoire fait partie de l'organisation NOAO, avec notamment le Kitt Peak National Observatory (KPNO) à Tucson, Arizona. L'observatoire possède plusieurs télescopes de petite taille, ainsi qu'un télescope de 4 mètres de diamètre : le télescope « Blanco », en l'honneur de Victor M. Blanco.

El Observatorio Interamericano de Cerro Tololo se ubica en el valle de Elqui, aproximadamente a 80 km de la ciudad de La Serena, en la Región de Coquimbo, Chile. Es operado por la Association of Universities for Research in Astronomy (AURA), consorcio de universidades privadas estadounidenses en colaboración con la National Optical Astronomy Observatories (NOAO), bajo convenio con la National Science Fundation y la Universidad de Chile.