SCISAT-1, also known as the Atmospheric Chemistry Experiment (ACE), is a Canadian satellite mission for remote sensing of the Earth's atmosphere. It was launched into low Earth circular orbit (altitude 650 km, inclination 74¿) on 12 Aug. 2003. The primary ACE instrument is a high spectral resolution (0.02 cm-1) Fourier Transform Spectrometer (FTS) operating from 2.2 to 13.3 ¿m (750--4400 cm-1). The satellite also features a dual spectrophotometer known as MAESTRO with wavelength coverage of 285--1030 nm and spectral resolution of 1--2 nm. A pair of filtered CMOS detector arrays records images of the Sun at 0.525 and 1.02 ¿m. Working primarily in solar occultation, the satellite provides altitude profile information (typically 10--100 km) for temperature, pressure, and the volume mixing ratios for several dozen molecules of atmospheric interest, as well as atmospheric extinction profiles over the latitudes 85¿N to 85¿S. This paper presents a mission overview and some of the first scientific results.