A theoretical study of the mechanisms and kinetics for the C4H6 system was carried out using ab initio molecular orbital theory based on the CCSD(T)/CBS// B3LYP/6-311++G(3df,2p) method in conjunction with statistical theoretical variable reaction coordinate transition-state theory and RRKIVI/ME calculations. The calculated results indicate that buta-1,3-diene, but-1-yne, and C4H5 + H can be the major products of the C-3 + C-1 reaction, while CCH2 + C(2)H(4 )and C4H5 + H play an important role in the C-2 + C-2 reaction. In contrast, the C4H6 fragmentation giving rise to C-3 + C-1 and C4H5 + H becomes the key reaction paths under any temperature and pressure. The rate constants for the system have been calculated in the 300-2000 K temperature range at various pressures for which the C-2 + C-2 -> C(4)H(6 )high-P limit rate constant, 10.24 X 10(14)T(-0.51 )cm(3)/mol/s, agrees well with the measured value of Hidaka et al., 9.64 X 10(14 )T(-0.5)cm(3)/mol/s. Also, the high-P limit rate constants of the channels but-2-yne -> 2-C4H5 + H and C-3 + C-1 -> C4H6, being 1.7 X 10(14) exp(-351.5 kJ.mol(-1)/RT) s(-1) and 5.07 X 10(13) exp(0.694 kj.mol(-1)/RT) cm(3)/mol/s, are in good agreement with the available literature data 5 X 10(14 )exp(-365.3 kJ.mol(-1)/RT) s(-1) and 4.09 X 10(13 )exp(1.08 kJ.mol(-1)/RT) cm(3)/mol/s reported by Hidaka et al. and Knyazev and Slagle, respectively. Moreover, the 298 K/50 Torr branching ratios for the formation of buta-1,2-diene (0.43) and but-1-yne (0.57) as well as the total rate constant 5.18 x 10(13) cm(3)/mol/s of the channels C-3 + C-1 -> buta-1,2-diene and C-3 + C-1 -> but-1-yne are in excellent accord with the laboratory values given by Fahr and Nayak, being 0.4, 0.6, and (9.03 +/- 1.8) x 10(13 )cm(3)/mol/s, respectively. Last but not least, the rate constants and branching ratios for the C4H6 dissociation processes in the present study also agree closely with the theoretically and experimentally reported data.