Deep exposures with the Hubble Space Telescope (HST) have provided the primary evidence that star-forming galaxies were present in the first billion years of cosmic history. Sometime during this early period the intergalactic medium transitioned from a neutral gas to one that is fully ionized. How did this `cosmic reionization' occur and were star-forming galaxies responsible? Imaging of deep fields with HST's Wide Field Camera 3 in conjunction with Spitzer photometry and Keck spectroscopy has provided important new insight into understanding when reionization occurred and the role of early galaxies in the process. Recent Planck results on the optical depth of electron scattering to CMB photons provide complementary information. I will review this rapid progress in our understanding of the last missing piece in our overall picture of cosmic history and discuss the remaining challenges ahead of future facilities such as JWST and E-ELT.