The isotopic invariance criterion, ab initio molecular orbital results, and principal component analysis are used to resolve the sign ambiguities of the dipole moment derivatives for cis-dichloroethylene and the out-of-plane derivatives of trans-dichloroethylene. Atomic polar tensors (APTs) for CiS-C2H2Cl2 and cis-C2D2Cl2 as well as out-of-plane polar tensor elements for trans-C2H2Cl2 and trans-C2D2Cl2 are reported. Mean dipole moment derivatives of the difluoro-and dichloroethylenes are compared and interpreted as atomic charges. The APTs of cis-dichloroethylene are transferred to trans-dichloroethylene to calculate its infrared fundamental vibrational intensities. These intensities are in much better agreement with the experimental intensities than those calculated by a MP2/6-311++G(d,p) wave function. The transferability of mean dipole moment derivatives between the cis and trans-dichloroethylenes is demonstrated using a simple potential model and carbon and chlorine core electron binding energies obtained by ESCA spectroscopy.