There can be no doubt that a peculiar amount of ignorance exists regarding the subject of sexual inversion. I know medical men of many years' general experience who have never, to their knowledge, come across a single case. We may remember, indeed, that some fifteen years ago the total number of cases recorded in scientific literature scarcely equaled those of British race which I have obtained, and that before my first cases were published not a single British case, unconnected with the asylum or the prison, had ever been recorded. Probably not a very large number of people are even aware that the turning in of the sexual instinct toward persons of the same sex can ever be regarded as inborn, so far as any sexual instinct is inborn. And very few, indeed, would not be surprised if it were possible to publish a list of the names of sexually inverted men and women who at the present time are honorably known in church, state, society, art, or letters. It could not be positively affirmed of all such persons that they were born inverted, but in most the inverted tendency seems to be instinctive, and appears at a somewhat early age. In any case, however, it must be realized that in this volume we are not dealing with subjects belonging to the lunatic asylum, or the prison. We are concerned with individuals who live in freedom, some of them suffering intensely from their abnormal organization, but otherwise ordinary members of society. In a few cases we are concerned with individuals whose moral or artistic ideals have widely influenced their fellows, who know nothing of the peculiar organization which has largely molded those ideals. I am indebted to several friends for notes, observations, and correspondence on this subject, more especially to one, referred to as "Z.," and to another as "Q.," who have obtained a considerable number of reliable histories for me, and have also supplied many valuable notes; to "Josiah Flynt" (whose articles on tramps in _Atlantic Monthly_ and _Harper's Magazine_ have attracted wide attention) for an appendix on homosexuality among tramps; to Drs. Kiernan, Lydston, and Talbot for assistance at various points noted in the text; and to Dr. K., an American woman physician, who kindly assisted me in obtaining cases, and has also supplied an appendix. Other obligations are mentioned in the text.