The results of the first year WMAP sky survey are full sky microwave maps in five frequency bands from 23 to 94 GHz. Calibration errors are < 0.5% and the low systematic error level is well specified. The cosmic microwave background (CMB) is separated from the foregrounds using the multifrequency data. The 2 ≤ l ≤ 900 anisotropy power spectrum is cosmic variance limited for l < 354 with a signal-to-noise ratio >1 per mode to l = 658. The temperature-polarization cross-power spectrum reveals both acoustic features and a large angle correlation from reionization. The optical depth of reionization is τ = 0.17 ± 0.04. A best-fit cosmological model to the CMB and other measures of large scale structure works remarkably well with only a few parameters. The age of the best-fit universe is t 0 = 13.7 ± 0.2 Gyr old. The matter density is Ω m h 2 = 0.135+0.008 --0.009, the baryon density is Ω b h 2 = 0.0224 ± 0.0009, and the total mass-energy of the universe is Ω tot = 1.02±0.02. For WMAP data alone, n s = 0.99 ± 0.04. The lack of CMB fluctuation power on the largest angular scales reported by COBE and confirmed by WMAP is intriguing. WMAP continues to operate, so results will improve.