Many of the lectures printed in this volume have formed the basis of a seriesgiven at Teachers College, Columbia University, during the summer sessions of1914 and 1915, and during the academic year 1914-1915. Others were addressedto parents, to groups of men, to women's clubs, and to conferences on sexeducation. In order to avoid extensive repetition, there has been somecombination and rearrangement of lectures that originally were addressed togroups of people with widely different outlooks on the sexual problems.Several years ago the late Dr. Prince A. Morrow announced that a volumedealing with many of the timely topics of sex-education was to be prepared bythe undersigned with the advice and criticism of a committee of the AmericanFederation for Sex-Hygiene; but even before Dr. Morrow's death it becameevident that this plan was impracticable. Three members (Morrow, Balliet,Bigelow) of the original committee collaborated in a report presented at the XVInternational Congress on Hygiene and Demography. Since that time the writer,working independently, has found it desirable to reorganize completely theoriginal outline announced by Dr. Morrow.In accordance with a declaration made voluntarily in a conversation with Dr.Morrow, the author considers himself pledged to devote all royalties from thisbook to the movement for sex-education.Among the many persons to whom is due acknowledgment of helpfulness inthe preparation of this book, the author is especially indebted for suggestions tothe late Dr. Prince A. Morrow, to Dr. William F. Snow, Secretary of theAmerican Social Hygiene Association, and to Dr. Edward L. Keyes, Jr.,President of the Society of Sanitary and Moral Prophylaxis; for constructivecriticism, to his colleagues, Professor Jean Broadhurst and Miss Caroline E.Stackpole, of Teachers College, who have read carefully both the originallectures and the completed manuscript; and to Olive Crosby Whitin (Mrs.Frederick H. Whitin), executive secretary of the Society of Sanitary and MoralProphylaxis, who has suggested and criticized helpfully both as a reader of themanuscript and as an auditor of many of the lectures delivered at TeachersCollege