[APS sponsored lecture]

Fifty years of progressively detailed measurements of the cosmic microwave background radiation (CMB) have transformed cosmology and fundamental physics. They have yielded a treasure of information about the formation and evolution of the Universe. During the last year several experiments announced the first measurements of the signature of gravitational waves on the polarization of the CMB. Ultimately, such measurements can probe an epoch of inflation that is hypothesized to occur as short as 10^-35 seconds after the big bang. They will also provide tight constraints on the mass of the neutrinos. I will discuss our current state of knowledge and give an outlook for the near future.