The conventional view that the human race consists of men and women does not stand up to strict scrutiny. There is no clear boundary between the two genders. There is a vast neutral space. It is filled with people who cannot be classified as either male or female. In the overwhelming majority, these are deeply unhappy people. They seem strange, “abnormal” to others; they cause bewilderment and sometimes even fear. But these are living people. Nature created them the way they are. Society is obliged to recognize the fact of their existence. And the first step towards this, the attempt made in this book, is to bring them together under the sign of a special, third gender, even if not officially recognized. The third gender is diverse in composition. Some of its representatives can be immediately guessed by their unusual body structure. Others, on the contrary, have no external differences. But in all cases there is a biological basis for this unusual gender identity. There is a peculiar psychology. And there are specific behavioral traits that largely depend not only on psychology, but also on the inability to find one’s rightful place in a society built on the interaction of the two main sexes. The author of the book, a famous psychiatrist, Professor A.I. Belkin for many decades provides medical assistance to representatives of the third gender. Before his eyes, the possibilities of medicine expanded significantly. But the position of these people in society has hardly changed. Too little is known about the third field, too many absurdities and fables are mixed up around it in the mass consciousness. The desire to protect his patients, to affirm their right to life and happiness forced the doctor to take up the idea. But the book “The Third Sex” is not only about this... It also reveals the mystery of the two sexes, which will probably never cease to tease the imagination. What is the essence of masculine and feminine principles? Should the two sexes move closer together or, conversely, increase the distance between them? The material in the book provides a fascinating opportunity to combine biological, social and socio-psychological approaches in the search for answers to these eternal questions. The book is addressed to everyone who tends to think about the mysteries of human and their own nature. It is written easily, complex scientific and philosophical problems are presented in a form accessible to the general reader.