High-precision quantum chemical calculations have been performed for atmospherically important halomethane derivatives including CF, CF3, CHF2, CH2F, CF2, CF4, CHF, CHF3, CH3F, CH2F2, CCl, CCl3, CHCl2, CH2Cl, CCl2, CCl4, CHCl, CHCl3, CH3Cl, CH2Cl2, CHFCl, CF2Cl, CFCl2, CFCl, CFCl3, CF2Cl2, CF3Cl, CHFCl2, CHF2Cl, and CH2FCl. Theoretical estimates for the standard enthalpy of formation at 0 and 298.15 K as well as for the entropy at 298.15 K are presented. The determined values are mostly within the experimental uncertainty where accurate experimental results are available, while for the majority of the considered heat of formation and entropy values the present results represent the best available estimates.