Chemical and structural information relating to the BeO-H2O system is discussed and correlated. The infrared spectra of α, β, and amorphous Be(OH)2 have been studied in the range 650 to 10,000 cm-1. These show that the constitution of the three hydroxides is similar. The spectra are interpreted to arise from the coupled vibrations of Be(OH)4 structural groups and from hydroxyl interactions. The hydroxyl vibrations are identified by spectroscopic shifts observed on partial deuteration and by means of spectroscopic-structural relations. Tentative assignments are made by comparing the spectra from BeO, Be(OH)2, and other systems containing similar structural groups. The complex nature of the spectra is discussed.