This paper reviews the results obtained in this laboratory in experimental studies of volume H−ion sources. Two techniques are discussed, emission spectroscopy and vacuum ultraviolet laser absorption spectroscopy. Time‐resolved detection of Balmer‐alpha emission has been used to study the excited‐state hydrogen atom population. Vacuum ultraviolet laser absorption spectroscopy has been used to measure the ground electronic state atomic and molecular hydrogen populations. The Balmer‐alpha emission exhibits a modulation in the intensity at a frequency of twice the exciting rf radiation. On the other hand, the laser absorption measurements show that the density of ground‐state hydrogen atoms does not vary significantly with the phase of the exciting rf. Measurements of the vibrational population summed over all rotational states give a vibrational temperature of 6200 K. However, there is no evidence of the ‘‘plateau’’ predicted in the distribution forv≥5.