The use of plants for therapeutic purposes dates back to the beginning of time. Ancient civilizations, such as Egypt, China, India and the Incas of the Americas knew well the medicinal properties of herbs and used them in the prevention and treatment of diseases. Through the writings of great physicians, such as Hippocrates and Dioscorides, much of this ancient art had survived to our times. Nowadays we are witnessing the revival of the herbal tradition. There is a great interest in using this tradition in order to develop and define new, natural drugs for human use.