Redshift 6, one billion years after the Big Bang, marks theend of the reionization epoch. A crucial question is whether the UV flux from young starbursts at this redshift is sufficient to achieve this reionzation. We have used the Lyman break technique to identify candidate star-forming galaxies at this redshift in deep HST/ACS images, including the Hubble Ultra Deep Field. We have recently pushed our sample to galaxies at redshifts 7-10 using new WFC3 images. Some of these z~6 galaxies exhibit Balmer breaks in mid-IR Spitzer data, indicating that a subset have evolved stellar populations even within the first billion years after the Big Bang, indicating star formation commenced at even higher redshifts. Spectroscopic confirmation of this population is crucial, to guard against low-redshift interlopers and to study the Lyman-alpha emission line properties of z~6 galaxies. We have undertaken the deepest spectroscopy yet to achieve this.