The Infrared Astronomical Satellite (IRAS)* has completed an unbiased all-sky survey at wavelengths from 10 to 100 Am. The design and performance of the focal plane array is described with emphasis on in-orbit measurements of the sensitivity and stability. In the four broad spectral bands centered at 12, 25, 60, and 100 Am, the system noise equivalent flux density (NEFD) values are, in Jy/Hz1/2, 0.03, 0.025, 0.046, and 0.21, respectively (Jansky = 10-26 W/m2/Hz). For point sources, a single scan at the survey rate of 3.8 arcmin/s yields limiting flux densities at the 3-sigma confidence level of 0.36, 0.30, 0.39, and 1.2 Jy. The dc stability of the junction field effect transistor (JFET) amplifiers and the excellent off-axis rejection of the tele-scope permit total flux measurements of extended infrared emission at levels below 106 Jy/sr. Response of the extrinsic silicon and germanium photo-detectors to ionizing radiation is described.