Located 40 km from San Pedro de Atacama, at an altitude of 5,190 metres (17,030 ft), it was one of the highest ground-based telescopes in the world.

Measurements of cosmic microwave background radiation (CMB) by experiments such as COBE, BOOMERanG, WMAP, CBI, the South Pole Telescope and many others, have greatly advanced our knowledge of cosmology, particularly the early evolution of the universe.

Detection of galaxy clusters and follow-up measurements in visible and X-ray light, provide a picture of the evolution of structure in the universe since the Big Bang.

High sensitivity observations of the cosmic microwave background radiation allow precision measurements of cosmological parameters, detection of galaxy clusters among other scientific goals, probing the early and late stages in the history of the evolution of the universe.

ACT is located in the dry and high (yet easily accessible) Chajnantor plateau in the Andean mountains in the Atacama Desert in northern Chile.

Due to the exceptional observing conditions of the Atacama Desert and its accessibility by road and nearby ports, several other observatories are located in the region, including CBI, ASTE, Nanten, APEX and ALMA.

The three lenses in ACT are made of cryogenically cooled anti-reflection coated silicon, a desirable material for instruments in the millimeter due to its high index of refraction (n=3).

Anti-reflection coatings in ACTPol and AdvACT are made of sub-wavelength structured metamaterial silicon, an innovation in ground based CMB telescopes at the time.

The detectors are superconducting transition-edge sensors, a technology whose high sensitivity allows measurements of the temperature of the CMB to within a few millionths of a degree.