The Atmospheric Infrared Sounder (AIRS) is one instrument in a suite of six instruments currently flying onboard NASA’s Earth Observing System (EOS) Aqua spacecraft. NASA’s Aqua spacecraft was launched successfully on May 4, 2002 from Vandenberg Air Force Base in California. AIRS is a cryogenic instrument developed under a Jet Propulsion Laboratory contract by BAe Systems formely Lockheed Martin Infrared Imaging Systems, for NASA. AIRS will provide new and more accurate data about the atmosphere, land and oceans, which provides a powerful new tool for climate studies and enables the advancement of weather prediction models. AIRS observations permit the measurement of the atmospheric temperature with an accuracy of 1 K in 1 km thick-layers in the troposphere and surface temperatures with an accuracy of 0.5 K. The Aqua spacecraft was placed in a sun-synchronous near-circular polar orbit with an inclination of 98.2 degrees, mean altitude of 705 km, 98.72 minute orbit period and 1:30 pm ascending node. The nominal on-orbit mission lifetime for the instrument is 6 years. AIRS measurements are based on passive infrared remote sensing using a precisely calibrated, high spectral resolution grating spectrometer with an infrared coverage from 3.7 to 15.4 μm. To achieve this high performance over this broad wavelength range, the spectrometer is cooled to 155 K and the Mercury Cadmium Telluride (HgCdTe) focal plane is cooled to 58 K. The detectors are cooled by a pair of long-life, low vibration, pulse tube mechanical coolers to 58 K, and a two-stage passive cooler with a deployable Earth shield provides cooling for the spectrometer to achieve a stable temperature near 155 K. This paper provides a general overview of the cryogenic system design and presents its on-orbit performance for the first year of operation.