Pyrolysis and oxidation of ethylene were studied behind reflected shock waves in the temperature range 1100-2100 K at pressures of 1.5-4.5 atm. Ethylene decay in both the pyrolysis and oxidation reactions was measured by using both time-resolved IR-laser absorption at 3.39 mu m and time-resolved IR-emission at 3.48 mu m. CO2 production in the oxidation was also measured by time-resolved IR-emission at 4.24 mu m. The production yields were also studied using a single pulse method. The pyrolysis and oxidation of ethylene were modeled using a kinetic reaction mechanism including the most recent mechanism for formaldehyde, ketene, methane, ethane, and acetylene oxidations. The present and some earlier shock tube data was reproduced using the proposed mechanism with 161 reaction steps and 51 species. The reactions and the rate constants in the mechanism were discussed in detail. It was found that reactions C2H4 + M --> C2H2 + H-2 + M, C2H4 + M --> C2H3 + H + M, C2H4 + C2H4 --> C2H3 + C2H5, C2H4 + H --> C2H3 + H-2, C2H4 + C2H3 --> 1, 3-C6H6 + H, C2H4 + O --> products and C2H3 + O-2 --> products were important to predict our data, which was with mixtures of wide composition from ethylene-rich to ethylene-lean.