Some twenty-five years ago the writer prepared the manuscript of a book which was published under the title "Dielectric Constant and Molecular Structure." " Dipole Moment" would have been used instead of "Dielectric Constant" had it not been for the unfamiliarity of the term to the scientific public. At that time it was possible to collect, correlate, and interpret virtually all the data on the subject available in the literature. Since then knowledge of the field has grown to such an extent that a completely new book is necessary. The number of dipole moment measurements now in the literature is too great to permit the complete and detailed discussion attempted twenty-five years ago. Moreover, the extensive work which has been carried out on the relations of dielectric constant and loss to structure and intermolecular forces can profitably be considered in connection with the relations between dipole moment and molecular structure.