High-level ab initio quantum chemical calculations have been used to investigate possible reactions in the Al-H-Cl system. Transition states or barrierless reaction paths have been identified for essentially all feasible reactions in this system involving a single aluminum atom. Structures, energies, and vibrational frequencies for reactants, products, and transition states in this system are presented. These results provide a basis for the estimation of reaction rate parameters for this system using transition state theory and related unimolecular reaction rate theories and thereby construct a reaction mechanism useful for detailed chemical kinetic modeling of aluminum combustion in HCl and chemical vapor deposition using AlCl3 in H-2. Tn the few cases where previous experimental or theoretical results have been published, the present work is consistent with previous work.