Hydrogen can be inadvertently introduced at any of several steps in the fabrication of optoelectronic devices. The most common consequence of hydrogenation is the passivation of dopant impurities, which leads to a decrease in the electrical conductivity of the material. The most successfully, applied experimental technique for directly determining the involvement of hydrogen has been infrared-absorption local vibrational mode (LVM) spectroscopy, Examples of LVM spectroscopy of hydrogen-related complexes are given for the compound semiconductors Gap, ZnSe, GaN, GaAs, and AlSb. Recent studies have utilized large hydrostatic pressures to probe the vibrational properties of hydrogen-related complexes.