In reviewing the literature that during the past decade has advocated sex-education, it has seemed to me that there is left little possibility of any decidedly new and important contribution to the arguments favoring such instruction, for the whole case has been splendidly presented by eminent writers in the fields of medicine, biology, sociology, and ethics. It now appears that the great majority of educators, scientists, and intelligent citizens in general have accepted the arguments for sex-instruction, so far as they have been informed concerning the meaning and need of the movement; and this leads me to the belief that in the future we need not new arguments but frequent restatements of the established facts which indicate the importance of widespread knowledge regarding the function that is inseparably connected with the perpetuation of life. In short, we now need a propagandism for extending the sex-education movement among the masses of people. For those who have already accepted sex-education, a survey of the facts that created a demand for sex-instruction will give a clearer outlook on the movement. The rapid increase of interest in sex-education has been the result of widespread dissemination of convincing facts concerning some common disharmonies that grow out of the sexual problems of the human race. These facts which have led to sex-education should be kept in mind by all who wish to understand or to play a part in the instruction of young people. It is quite unnecessary, and still more undesirable, to recite at length in these lectures the social, medical, and psycho-pathological facts concerning abnormal or perverted sexual processes. Fortunately, the educational ends may be gained by a general review that points out the bearings of the main lines of the sexual problems, the misunderstandings and mistakes that education may help prevent and correct. [Sidenote: Parents should know reasons for sex-instruction.] It is important that the general public, especially the parents, should understand the reasons which have induced numerous physicians, ministers, and educators to become active advocates of systematic sex-instruction for young people. Although the movement has made extensive progress in the ten years of propagandic work, is probably true that the majority of even intelligent parents are not yet convinced that their children need sex-instruction. This is due largely to the fact that the parents have not yet been shown the reasons why it is now, and always has been, unsafe to allow children to gain more or less sexual information from unreliable and vulgar sources. In fact, it is surprising to find many parents, especially mothers, who seem unable to grasp the idea that their "protected" children can possibly get impure information.