The excited state processes of an acetyltriphenylgermane as well as the generation and the reactivity of the germyl radical are studied by laser. ash photolysis, ESR spin trapping experiments and MO calculations. The transient spectra, the dissociation quantum yield, the singlet excited state S-1 lifetime, the S-1 quenching by an iodonium salt, the triplet state energy level E-T, the Ge-C bond dissociation energy BDE, the interaction of the germyl radical with oxygen, double bonds and an iodonium salt, and the ESR spectra are determined. A triplet cleavage process is clearly evidenced; a singlet cleavage should likely contribute. The overall reactivity is discussed and compared to that of parent compounds. The acetyltriphenylgermane behaves as a high performance photoinitiator in the free radical polymerization and free radical promoted cationic polymerizations. (C) 2009 Elsevier B. V. All rights reserved.