U. Vianna Filho In his historical evolution, man has been able to dominate nature by means of his technological achievements, his knowledge and his inventiveness, attaining an increasing control over the world and its organization. As a result, his power over his fellow men has also increased, giving him more, and more responsibility which leads, of necessity, to one existential problem: is the contemporary man, with all his power and knowledge, really happy? Technological progress has brought him several rights and desires: health, better insight into the future and greater control over his own des tiny, but despite all this he still suffers from insecurity and from all the new problems that he has to face, which fact accounts for his imperfections and limitations that inevitably generate anxiety. Anxiety, therefore, constitutes one of the main characteristics of modern man. It can be foreseen today that, in the near future, the entire population of any large city will suffer from anxiety and behave in a 'neurotic' way. Man is seeking relief from pain, suffering and, naturally, also anxiety. Thus all possible efforts are being made to find a solution for this anxiety. The search for substances that are able to eliminate anxiety is one of the constant concerns of modern science, and, in this context, one of the turn ing points, as we will see in this volume, has been the discovery of the chemi cal agents known as the benzodiazepines."