Ozonation of various silanes and germanes produced the corresponding hydrotrioxides, R-3-SiOOOH and R3GeOOOH, which were characterized by H-1, C-13, O-17, and Si-29 NMR, and by infrared spectroscopy in a two-pronged approach based on measured and calculated data. Ozone reacts with the E-H (E = Si, Ge) bond via a concerted 1,3-dipolar insertion mechanism, where, depending on the substituents and the environment (e.g., acetone-d(6) solution), the H atom transfer precedes more and more E-O bond formation. The hydrotrioxides decompose in various solvents into the corresponding silanols/germanols, disiloxanes/cligermoxanes, singlet oxygen (O-2((1)Delta(g))), and dihydrogen trioxide (HOOOH), where catalytic amounts of water play an important role as is indicated by quantum chemical calculations. The formation of HOOOH as a decomposition product of organometallic hydrotrioxides in acetone-d6 represents a new and convenient method for the preparation of this simple, biochemically important polyoxide. By solvent variation, singlet oxygen (O-2((1)Delta(g))) can be generated in high yield.