The study of auto-erotism is far from being an unimportant or merely curious study. Yet psychologists, medical and non-medical, almost without exception, treat its manifestations--when they refer to them at all--in a dogmatic and off-hand manner which is far from scientific. It is not surprising, therefore, that the most widely divergent opinions are expressed. Nor is it surprising that ignorant and chaotic notions among the general population should lead to results that would be ludicrous if they were not pathetic. To mention one instance known to me: a married lady who is a leader in social-purity movements and an enthusiast for sexual chastity, discovered, through reading some pamphlet against solitary vice, that she had herself been practicing masturbation for years without knowing it. The profound anguish and hopeless despair of this woman in face of what she believed to be the moral ruin of her whole life cannot well be described. It would be easy to give further examples, though scarcely a more striking one, to show the utter confusion into which we are thrown by leaving this matter in the hands of blind leaders of the blind. Moreover, the conditions of modern civilization render auto-erotism a matter of increasing social significance. As our marriage-rate declines, and as illicit sexual relationships continue to be openly discouraged, it is absolutely inevitable that auto-erotic phenomena of one kind or another, not only among women but also among men, should increase among us both in amount and intensity. It becomes, therefore, a matter of some importance, both to the moralist and the physician, to investigate the psychological nature of these phenomena and to decide precisely what their attitude should be toward them. I do not purpose to enter into a thorough discussion of all the aspects of auto-erotism. That would involve a very extensive study indeed. I wish to consider briefly certain salient points concerning auto-erotic phenomena, especially their prevalence, their nature, and their moral, physical, and other effects. I base my study partly on the facts and opinions which during the last thirty years have been scattered through the periodical and other medical literature of Europe and America, and partly on the experience of individuals, especially of fairly normal individuals.