In this treatise, the veteran Swedish reformer attacks problems the most vital to the welfare of the human race, problems which have throughout the centuries engaged the attention of leaders of thought. The writers who have given attention to the complex subject of the relations of the sexes, of the obligations of the state in the control of these relations, and of the organisation of the family as the foundation of society, include such authors as Plato, Goethe, Richter, Rousseau, Mary Wollstonecraft, Fourier, Comte, Mrs. Browning, Mill, Ibsen, Westermarck, Charlotte Gilman, Havelock Ellis, and many others. These problems are complex, and the difficulties presented by them most serious. No writer has ever yet presented solutions that could be accepted as finally satisfactory. Ellen Key writes with a profound antagonism to the philistinism and hypocrisy which have characterised much of the consideration given by the community to the subjects. She points out (as has, of course, been emphasised by many earlier writers) that the ignoring of an evil does not dispose of it, and thativ so far from preserving society from its influence, the burying of an evil merely tends to increase its corrupting and demoralising results. Whether or not the reader be prepared to accept the conclusions and recommendations of the Swedish thinker, he must recognise that these conclusions represent the result of painstaking and scholarly thought and investigation. Daring and iconoclastic as they may be, the views of Ellen Key are presented with a calmness and philosophy of method that is absolutely free from any trace of sensationalism. The book, which is being distributed in half a dozen languages to a world's public, must be accepted as a most important contribution to philosophic thought. The introduction by Havelock Ellis, himself an authority on social problems, will help to make clear its purpose and character. New York, January, 1911.