High-temperature oxidation of acetylene, above about 1000 K, is addressed numerically and theoretically. A new detailed-chemistry description is employed that involves 114 elementary steps among 28 chemical species, revising questionable rate parameters for certain elementary steps, notably concerning OH and O-2 attack on C2H2. It proceeds most importantly through ketyl at the highest temperatures and vinyl at lower temperatures, and it is shown to yield reasonable agreement with shock-tube ignition results. A short mechanism of 21 steps, 4 of which are reversible, among 15 species, is derived from the detailed-chemistry description by sensitivity and reaction-path analyses, for use above a temperature that increases with pressure and that is about 1200 K at 1 bar. Through systematic application of steady-state and partial-equilibrium approximations, a seven-step reduced mechanism is derived from the short mechanism, involving four steps that are important during the induction process leading to ignition and three that are important during the slower further heat release that follows ignition. The four induction steps are an example of branched-chain thermal-explosion chemistry. They are simplified systematically to a one-step approximation from which an explicit formula is derived determining the ignition time, in good agreement with predictions of the short and reduced mechanism. By treating the three slow heat-release steps as a one-step recombination-controlled process, a two-step approximation is then obtained for the complete detonation. These various levels of description of acetylene ignition and detonation chemistry can be helpful in computational and theoretical studies of high-temperature ignition and detonation behavior of fuels that contain or produce appreciable amounts of acetylene. (C) 2001 by The Combustion Institute.