The cosmic microwave background (CMB) is one of only a few physically observable remnants of the early Universe. Studies of the spectrum, polarization and spatial distribution of the CMB can potentially lead to a detailed understanding of the processes that took place in the early Universe. Many of the outstanding cosmological questions regarding the age, contents, future, and large scale dynamics of the universe are addressed in these studies. In particular, measurements of the spatial anisotropy of the CMB are a very effective method for testing and constraining models of cosmic structure formation.