Cosmology confronts some of the most fundamental questions in the whole of science. How and when did our universe begin? What is it made of? How did galaxies and other structures form? There has been enormous progress in the past few decades towards answering these questions. For example, recent observations have established that our universe contains an unexpected mix of components: ordinary atoms, exotic dark matter and a new form of energy called dark energy. Gigantic surveys of galaxies reveal how the universe is structured. Large supercomputer simulations recreate the evolution of the universe and provide the means to relate processes occurring near the beginning with observations of the universe today. A coherent picture of cosmic evolution, going back to a tiny fraction of a second after the Big Bang, is beginning to emerge. However, fundamental issues, like the identity of the dark matter and the nature of the dark energy, remain unresolved.