The structural data, vibrational assignments, enthalpies of vaporization and formation for chloromethane, dichloromethane, trichloromethane, tetrachloromethane, fluoromethane, difluoromethane, trifluoromethane, and tetrafluoromethane were critically reviewed. Based on the selected best values, the thermodynamic properties for each of these eight chloro‐ and fluoromethanes were calculated by statistical thermodynamic methods using the rigid‐rotor harmonic‐oscillator approximations. The derived entropies and heat capacities are compared with the available third law entropies and vapor heat capacities. The calculated values ofCpo, So, and &Dgr;Hfoat 298.15 and 700 K are compared with those reported in the other major compilations.