The Spitzer Wide-area InfraRed Extragalactic survey (SWIRE), the largest Spitzer Legacy program, is a wide-area, imaging survey to trace the evolution of dusty, star-forming galaxies, evolved stellar populations, and AGN as a function of environment, from redshifts z~3 to the current epoch. SWIRE surveys 6 high-latitude fields, totaling ~50 sq. deg. in all 7 Spitzer bands: 3.6, 4.5, 5.8, and 8 microns with IRAC and 24, 70, and 160 microns with MIPS (Lonsdale et al. 2003). The SWIRE Legacy Extragalactic Source Catalogs will eventually contain in excess of 2 million IR-selected galaxies, from those dominated by the light of stellar populations detected primarily by IRAC, to starbursts, ultra-luminous infrared galaxies and AGN detected also by MIPS.