The Atmospheric Chemistry Experiment (ACE), also called SCISAT, is a Canadian-led small satellite mission for remote sensing of the Earth’s atmosphere. ACE was launched into a low Earth circular orbit by NASA on August 12, 2003 and it continues to function nominally. The ACE instruments are a high spectral resolution (0.02cm−1) Fourier Transform Spectrometer (FTS) operating from 2.2 to 13.3μm (750–4400cm−1), a spectrophotometer known as Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation (MAESTRO) with wavelength coverage of 285–1020nm and two filtered detector arrays to image the Sun at 0.525 and 1.02μm. ACE operates in solar occultation mode to provide altitude profiles of temperature, pressure, atmospheric extinction and the volume mixing ratios (VMRs) for several dozen molecules and related isotopologues. This paper presents a mission overview and a summary of selected scientific results.