The Cosmic Background Explorer, launched November 18, 1989, has nearly completed its first full mapping of the sky with all three of its instruments: a Far Infrared Absolute Spectrophotometer (FIRAS) covering 0.1 to 10 mm, a set of Differential Microwave Radiometers (DMR) operating at 3.3, 5.7, and 9.6 mm, and a Diffuse Infrared Background Experiment (DIRBE) spanning 1 to 300 &mgr;m in ten bands. A preliminary map of the sky derived from DIRBE data is presented. Initial cosmological implications include: a limit on the Comptonizationyparameter of 10−3, on the chemical potential &mgr; parameter of 10−2, a strong limit on the existence of a hot smooth intergalactic medium, and a confirmation that the dipole anisotropy has the spectrum expected from a Doppler shift of a blackbody. There are no significant anisotropies in the microwave sky detected, other than from our own galaxy and a cos &thgr; dipole anisotropy whose amplitude and direction agree with previous data. At shorter wavelengths, the sky spectrum and anisotropies are dominated by emission from ‘local’ sources of emission within our Galaxy and Solar System. Preliminary comparison ofIRASandDIRBEsky brightnesses toward the ecliptic poles shows theIRASvalues to be significantly higher than found byDIRBEat 100 &mgr;m. We suggest the presence of gain and zero‐point errors in theIRAStotal brightness data. The spacecraft, instrument designs, and data reduction methods are described.