With his new work, Professor Apostolos Georgiadis attempted to write the textbook he wished he had read when he was young and starting his studies at the Law School of Athens. This book seeks purposes different from the well-known "Introductions to Law," which primarily aim to familiarize non-lawyers with the basic concepts of law and its various branches. Its orientation is partly different in relation to "Legal Methodology" or "Methodology of Law," which has as its main focus the methods of legal reasoning during the process of interpreting and applying legal rules in practice.