As recently as 1906 W. Fliess (Der Ablauf des Lebens) has claimed ownership of the idea of bisexuality (in the sense of double sex). Psychoanalytic investigation very strongly opposes the attempt to separate homosexuals from other persons as a group of a special nature. By also studying sexual excitations other than the manifestly open ones it discovers that all men are capable of homosexual object selection and actually accomplish this in the unconscious. Indeed the attachments of libidinous feelings to persons of the same sex play no small rôle as factors in normal psychic life, and as causative factors of disease they play a greater rôle than those belonging to the opposite sex. According to psychoanalysis, it rather seems that it is the independence of the object, selection of the sex of the object, the same free disposal over male and female objects, as observed in childhood, in primitive states and in prehistoric times, which forms the origin from which the normal as well as the inversion types developed, following restrictions in this or that direction. In the psychoanalytic sense the exclusive sexual interest of the man for the woman is also a problem requiring an explanation, and is not something that is self-evident and explainable on the basis of chemical attraction. The determination as to the definite sexual behavior does not occur until after puberty and is the result of a series of as yet not observable factors, some of which are of a constitutional, while some are of an accidental nature. Certainly some of these factors can turn out to be so enormous that by their character they influence the result. In general, however, the multiplicity of the determining factors is reflected by the manifoldness of the outcomes in the manifest sexual behavior of the person. In the inversion types it can be ascertained that they are altogether controlled by an archaic constitution and by primitive psychic mechanisms. The importance of the _narcissistic object selection_ and the _clinging_ to the erotic significance of the _anal_ zone seem to be their most essential characteristics. But one gains nothing by separating the most extreme inversion types from the others on the basis of such constitutional peculiarities. What is found in the latter as seemingly an adequate determinant can also be demonstrated only in lesser force in the constitution of transitional types and in manifestly normal persons. The differences in the results may be of a qualitative nature, but analysis shows that the differences in the determinants are only quantitative. As a remarkable factor among the accidental influences of the object selection, we found the sexual rejection or the early sexual intimidation, and our attention was also called to the fact that the existence of both parents plays an important rôle in the child's life. The disappearance of a strong father in childhood not infrequently favors the inversion. Finally, one might demand that the