The first stars have long attracted cosmological interest, owing to their potential role in reionizing the intergalactic medium at high redshift. Because the first metal-free massive stars had smaller radii, hotter cores, and higher surface temperatures, they were prodigious emitters of ionizing photons, and may dominate He II reionization (4 Rydberg continuum). I will review our recent theoretical studies of these first stars, their nebular emission, and the escape of ionizing radiation from early galaxies into the IGM. I will conclude by assessing the prospects for detecting metal-free stellar populations with He II 1640 A and 4686 A recombination lines in proto-galaxies. These observations are feasible out to z = 3-5 with current technology on 10m telescopes. Higher-redshift surveys could be done with SIRTF and NGST.