High level ab initio electronic structure theory has been used to calculate the heats of formation of CCl and CCl2. The calculations were done at the CCSD(T) level with new correlation-consistent basis sets up through augmented hextuple-zeta including tight d functions on the Cl and then extrapolated to the complete basis set limit. Additional corrections for core/valence-correlation, relativistic effects both scalar and atomic spin-orbit, and zero-point energies have been included. The heat of formation at 0 K of CCl is 103.1 +/-0.4 kcal/mol and that of CCl2 is 55.1 +/-0.4 kcal/mol.