We have studied the deposition of aluminum films by triisobutylaluminum (TIBA) pyrolysis on clean and oxidized Si(lll) (7×7), Si(100) (2×1), and an evaporated aluminum film on silicon. On all of the silicon surfaces, HBA has a very low reaction probability (<0.01). On aluminum, the reaction probability is much higher, and the rate of steady state aluminum deposition is limited by β-hydride elimination from surface-bound isobutyl species to give isobutene and hydrogen. In the steady state deposition of aluminum on top of silicon, gas phase silanes such as isobutyl- and diisobutylsilane are also evolved. This clearly indicates that hydrogen and alkyl ligand transfer from aluminum to silicon (which has diffused up through the growing aluminum film) can occur. We have also found that alkyl species generated on aluminum surfaces by. the adsorption of alkyl iodides have surface chemistries analogous to the aluminum alkyl ligands.