Pyrolysis and oxidation of diacetylene were studied behind reflected shock waves in the temperature range 1100 to 2000 K at pressures of 1.1 to 2.6 atm. The product yields were studied by analyzing the reacted gas mixtures. The progress of the oxidation reaction was also observed using time-resolved IR-emission (4.24 mum) and UV-absorption (306.7 nm) methods. The main products observed in the pyrolysis with or without H-2 were acetylene and hydrogen. In fuel-rich oxidation, it was found that CO, H-2, and C2H2 were the main intermediates. The pyrolysis and oxidation of diacetylene were modeled using a kinetic reaction mechanism including recent sub-mechanisms for formaldehyde, ketene, acetylene, ethylene, and ethane oxidation. The present and earlier shock tube data were reproduced by a proposed mechanism with 174 reaction steps and 51 species. It was found that the reactions C4H2 + O-2 --> products, C4H2 + H + M --> IC4H3 + M, C4H2 + O --> C3H2 + CO, C4H2 + O --> C4HO + H, and C4H2 + OH --> C4H2O + H were important to predict our data in a wide-range of mixtures from diacetylene-rich (including diacetylene pyrolysis) to diacetylene-lean oxidation.