The thermal decomposition of triacetone triperoxide (TATP) was investigated over the temperature range 151 to 230degreesC and found to be first order out to a high degree of conversion. Arrhenius parameters were calculated: activation energy, 151 kJ/mol and pre-exponential factor, 3.75 X 10(13) s(-1). Under all conditions the principle decomposition products were acetone (about 2 mole per mole TATP in the gas-phase and 2.5 - 2.6 mole per mole in condensed-phase) and carbon dioxide. Minor products included some ascribed to reactions of methyl radical: ethane, methanol, 2-butanone, ethyl acetate; these increased at high temperature. Methyl acetate and acetic acid were also formed in the decomposition of neat TATP; the former was more evident in the gas-phase decompositions (151degreesC and 230degreesC) and the latter in the condensed-phase decompositions (151 degreesC). The decomposition of TATP in condensed-phase or in hydrogen-donating solvents enhanced acetone production, suppressed CO2 production, and slightly increased the rate constant (a factor of 2-3). All observations were interpreted in terms of decomposition pathways initiated by O-O homolysis.