One of the biggest questions in cosmology and physics today is whether string theory is the correct description of nature. There is very little in the way of experimentally-verifiable predictions that are forthcoming from string theory. There is, however, one observation —the measurement of the curvature of the universe —that could deliver a serious blow to string theory's hopes. And there is no better instrument to perform this measurement than the European Space Agency's Planck satellite, a probe designed to map the Cosmic Microwave Background (CMB) with extraordinary precision. With Planck in focus, this chapter tackles the history and the intricacies of CMB research and the issue of just how cosmologists are going to answer some very vexing questions: Why our universe is the way it is? Are there other universes? And if so, how will we know?