The present sixth edition is delivered updated until January 1, 2021. The update was made in collaboration with Katerina Savvaïdou, Associate Professor at the Law School of Aristotle University of Thessaloniki, Lawyer, who contributed mainly to Chapter C, Andreas Tsourouflis, Associate Professor at the Law School of the National and Kapodistrian University of Athens, Lawyer, who contributed mainly to Chapters A, B, C, D, and St, and Petros Pantazopoulos, PhD, Associate at the National and Kapodistrian University of Athens, Lawyer, who contributed mainly to Chapter E. The responsibility for the opinions, as well as for any errors or omissions, lies exclusively with the undersigned. In the 6th edition of the book "Tax Law", the entire subject matter of tax law is systematically examined, i.e. the concept and distinctions of taxes, the constitutional basis and limits of tax authority, the Greek tax system, international and European tax law, administrative tax procedure, and the framework of judicial protection in tax disputes. It is a useful and fully updated legislative and jurisprudential reference handbook for students, legal professionals, and professionals in general who deal with tax law.