Not only among laymen but also among serious thinkers and writers on medical topics the opinion is generally prevalent that there is a vast difference in the degree of intensity of the sex-impulse in men and women. Upon this supposition rests the justification of the double standard of sexual morality of the two sexes. If the intensity of the amatory emotions is the same in both sexes, then there is no justification for a double standard of sexual morality. Now, an emotion is, in its nature, subjective. Its intensity can never be objectively determined. Men and women may dispute the question of the different degree of intensity of the amatory emotions till the end of time, still they will never reach a definite conclusion. The only way to determine the nature of an emotion is to study its pathology. If it can be shown that the same pathological entities of the sex-instinct are found in men and women, the inference is justified that the normal emotions are also the same or similar in both sexes. To prove the similarity or identity of the intensity of the sex-impulse in both sexes, the author published several books dealing with the amatory emotions of men and of women, with the need of proper sexual instruction for children, and the causes of sexual impotence. It occurred to the author that if the amatory emotions are the same in men and women they ought to be treated together in one volume. Hence the present work. But, while the books referred to are the basis for several chapters of "Love," still every author grows with his work. After years of study of the subject of sex, the author was able to expand the sphere of his previous efforts so that readers will find some new points in this book of value and interest. If the reader should agree with this opinion, the author will consider himself well paid for his labors.