Observations of the cosmic microwave background, the radiation left over from the Big Bang, are snapshots of the universe as it was only three hundred thousand years after the Big Bang. These observations have addressed many of the issues that have driven cosmology over the past decades: How old is the universe? What is its shape and size? What is the composition of the universe? How do galaxies emerge? In this lecture, David Spergel focuses on the results from NASA´s Wilkinson Microwave Anistropy Probe (WMAP) and upcoming measurements from ESA´s PLANK satellite. While there has been significant progress, many key cosmological questions remain unanswered: What happened during the first moments of the Big Bang? What is dark energy? What were the properties of the first stars? Spergel discusses how future observations may start to answer these new and deeper questions.