It is a great honour for the Gratianus Series to publish the classic book of Professor Javier Hervada on Natural Law. While in many quarters Natural Law had become a bad word, not to be pronounced, and many years ago some pretended that this foundational branch of the legal system was dead, the intellectual reality is very different. If the contribution of Natural Law is not considered, legislators end up producing a legislative cacophony and judges transform their most unheard-of conceptions into judgments in which nothing counts and any caprice can be considered a right, as it has been manifested in several countries in recent years.