The cosmic microwave background (CMB) consists of radiation that was emitted before the formation of stars, galaxies, and all other classically observable structures in the universe. These CMB photons have expanded and cooled with the evolving universe but have interacted very little with matter since they were emitted. This radiation can therefore be viewed as a clean snapshot of the initial conditions for structure formation and contains a wealth of information about the nature of the universe at a time when it was a far less complex place than it is today. I will address the origin of the CMB and discuss how observations of this important relic provide cosmologists with a unique and powerful insight into the geometry, composition, expansion history, and age of our universe.