Pyrolysis and oxidation of acetylene were studied behind reflected shock waves in the temperature range 1100-2000 K at pressures of 1.1-2.6 atm analyzing the reacted gas mixtures. The progress of the oxidation reaction was also observed with real-time spectroscopy. Main products in the pyrolysis with H-2 or without H-2 were vinylacetylene, diacetylene, and triacetylene. In the oxidation with fuel-rich mixtures, it was found that CO was the main product, and C-1 and C-3 carbon species appeared. The pyrolysis and oxidation of acetylene were modeled using a kinetic reaction mechanism, including the most recent mechanism for formaldehyde and ketene oxidations. The present and earlier shock tube data were reproduced by a proposed mechanism with 103 reaction steps and 38 species. It was found that reactions C2H2 + O-2 --> CHO + CHO or C2H2 + O-2 --> CHCO + OH and C2H2 + CH2 --> C3H4 were important to predict our data in a wide range of mixtures from acetylene pyrolysis to acetylene-lean oxidation.