The Wilkinson Microwave Anisotropy Probe (WMAP) has made an accurate full-sky measurement of the microwave background temperature and polarization fluctuations. These measurements probe both the physics of the very early universe and the basic properties of the universe today. The WMAP measurements rigorously test our standard cosmological model and provide an accurate determination of basic comological parameters (the curvature of the universe, its matter density and composition). When combined with other astronomical measurements, the measurements contrain the properties of the dark energy and the mass of the neutrino. The observations also directly probe the physics of inflation: the current data imply that the primordial fluctuations were primarily adiabatic and nearly scale invariant.