Psychology is now recognizing the forces concealed in the human organism. In the long process of adaptation to social life, men have had to harness the wishes and desires born of these inner energies, the greatest and most imperative of which are Sex and Hunger. From the beginning of time, men have been driven by Hunger into a thousand activities. It is Hunger that has created "the struggle for existence." Hunger has spurred men to the discovery and invention of methods and ways of avoiding starvation, of storing and exchanging foods. It has developed primitive barter into our contemporary Wall Streets. It has developed thrift and economy,--expedients whereby humanity avoids the lash of King Hunger. The true "economic interpretation of history" might be termed the History of Hunger. But no less fundamental, no less imperative, no less ceaseless in its dynamic energy, has been the great force of Sex. We do not yet know the intricate but certainly organic relationship between these two forces. It is obvious that they oppose yet reinforce each other,--driving, lashing, spurring mankind on to new conquests or to certain ruin. Perhaps Hunger and Sex are merely opposite poles of a single great life force. In the past we have made the mistake of separating them and attempting to study one of them without the other. Birth Control emphasizes the need of re-investigation and of knowledge of their integral relationship, and aims at the solution of the great problem of Hunger and Sex at one and the same time. In the more recent past the effort has been made to control, civilize, and sublimate the great primordial natural force of sex, mainly by futile efforts at prohibition, suppression, restraint, and extirpation. Its revenge, as the psychoanalysts are showing us every day, has been great. Insanity, hysteria, neuroses, morbid fears and compulsions, weaken and render useless and unhappy thousands of humans who are unconscious victims of the attempt to pit individual powers against this great natural force. In the solution of the problem of sex, we should bear in mind what the successful method of humanity has been in its conquest, or rather its control of the great physical and chemical forces of the external world. Like all other energy, that of sex is indestructible. By adaptation, control and conscious direction, we may transmute and sublimate it. Without irreparable injury to ourselves we cannot attempt to eradicate it or extirpate it.