A space observation system that consists in an array of large 40-foot (12-meter) radio telescopes installed in the Atacama desert of northern Chile. The high precision telescopes, 66 initially, are linked together to make up the world's largest radio telescope to observe at millimetre and submillimeter wavelengths. Emissions at these levels have wavelengths longer than infrared, but shorter than radio waves and are invisible to the naked eye.

ALMA is developed jointly by an international partnership between Europe, North America and East Asia in cooperation with the Republic of Chile. Since a high and dry site is crucial to operations of millimetre wavelength the array is constructed on the Chajnantor plateau at 5000 metres height.