Gaussian-2 and QCI theory with basis sets up to 6-311+G(3df,2p) have been employed to obtain information about the carbenes (methylenes) CH2, CHBr, CHCl, CHF, CHI, CBr2, CBrCl, CBrF, CBrI, CCl2, CClF, CClI, CF2, and CI2. Geometries and vibrational frequencies for the singlet and tripler states, and the singlet-triplet splittings, have been characterized and are discussed in the context of the electronegativities of the substituents. Isodesmic reactions were used to derive a consistent set of enthalpies of formation for the 14 halocarbenes. Where there are measurements, the computed results compare well, and substantial gaps in the current literature are filled.