Brant Robertson

With the installation of the new Wide Field Camera 3 on the Hubble Space Telescope in 2009, we've experienced a rapid expansion in our knowledge of galaxies at extremely high redshifts. In the Hubble Ultra Deep Field, the deepest single field observed with HST, we now have found galaxies at redshifts z>7 when the universe was younger than a billion years old. I'll review our current knowledge of high-redshift galaxy populations and the constraints they place on the reionization history of the universe. I'll then describe a new HST program to increase the depth of the UDF by more than a factor of two that promises to find the most distant galaxies yet discovered.