The whole is written simply, and for the ordinary untrained reader, though it embodies some observations which will be new even to those who have made scientific researches on the subjects of sex and human physiology. These observations I intend to supplement and publish at greater length and in more scientific language in another place. I do not now touch upon the many human variations and abnormalities which bulk so largely in most books on sex, nor do I deal with the many problems raised by incurably unhappy marriages. In the following pages I speak to those--and in spite of all our neurotic literature and plays they are in the great majority--who are nearly normal, and who are married or about to be married, and hope, but do not know how, to make their marriages beautiful and happy. To the reticent, as to the conventional, it may seem a presumption or a superfluity to speak of the details of the most complex of all our functions. They ask: Is not instinct enough? The answer is No. Instinct is _not_ enough. In every other human activity it has been realised that training, the handing on of tradition are essential. As Dr. Saleeby once wisely pointed out: A cat knows how to manage her new-born kittens, how to bring them up and teach them; a human mother does not know how to manage her baby unless she is trained, either directly or by her own quick observation of other mothers. A cat performs her simple duties by instinct; a human mother has to be trained to fulfil her very complex ones. The same is true in the subtle realm of sex. In this country, in modern times, the old traditions, the profound primitive knowledge of the needs of both sexes, have been lost, and nothing but a muffled confusion of individual gossip disturbs a silence, shamefaced or foul. Here and there, in a family of fine tradition, a youth or maiden may learn some of the mysteries of marriage, but the great majority of people in our country have no glimmering of the supreme human art, the art of love; while in books on advanced Physiology and Medicine the gaps, the omissions, and even the misstatements of bare fact are amazing. In my first marriage I paid such a terrible price for sex-ignorance that I feel that knowledge gained at such a cost should be placed at the service of humanity. In this little book average, healthy, mating creatures will find the key to the happiness which should be the portion of each. It has already guided some to happiness, and I hope it may save some others years of heartache and blind questioning in the dark. MARIE CARMICHAEL STOPES. AUTHOR'S PREFACE TO FOURTH EDITION.