How microwave background observations probe physical conditions in the early universe is reviewed and the relationship between initial conditions and the statistical properties of CMB Fluctuations is discussed. The sensitivity of the angular power spectrum to the basic properties of the universe: its geometry, the abundance of atoms and dark matter, and the amplitude of initial fluctuations is discussed and the recent results from the Wilkinson Microwave Anisotropy Probe are reviewed. The predictions of the WMAP best fit model are compared with other astronomical observations.