The effect of atomic hydrogen on silicon grain boundaries is reviewed along with recent scanned spot methods for measuring the minority carrier recombination velocity, s, at grain boundaries. Measurements on a large number of grain boundaries in Honeywell silicon-on-ceramic are presented which show that s typically changes from ~ 2 x 105cm/sec to 3 x 103cm/sec, or less, after a few minutes exposure to an intense atomic hydrogen source. Electron-Beam-Induced-Current data on numerous grain boundaries are discussed ; these show that the differences in barrier height reduction from boundary to boundary in response to an external hydrogen source present at the sample surface are due to differences in boundary properties and not to fluctuations in the treatment conditions. The results of applying the Kaufman ion source passivation method to Edge Fed Growth ribbon solar cells indicate that substantial efficiency increases can be achieved in these devices with only a few minutes exposure to the hydrogen ion beam