Over its seven-month span, IRAS surveyed the sky twice over, at mid-infrared and far-infrared wavelengths. These all-sky surveys were the first of their kind and opened many new avenues of astronomical study. Among its most significant scientific achievements were the discovery of a new class of very bright galaxies that emit the vast majority of their light at infrared wavelengths; the identification of stellar nurseries, heavily obscured by dusty gas clouds, where new stars are being born; and the discovery and mapping of so-called “infrared cirrus,” vast clouds of very sparse interstellar gas and dust that glow faintly at far-infrared wavelengths.