The book "Multilevel Protection of the Principle of Legality in Criminal Law" offers a comprehensive analysis of the simultaneous protection of fundamental rights through various norms and jurisdictional bodies. It particularly highlights the multilevel protection of the principle of legality in criminal law. Written by recognized experts in the fields of criminal law, constitutional law, international public law, and legal philosophy, including many former advisors to the Spanish Constitutional Court, the work addresses various aspects of the principle of legality, such as the requirement of precision, judicial adherence to the law, and the prohibition of "ne bis in idem." The authors combine theoretical perspectives with a comparative approach that incorporates the case law of the European Court of Human Rights, the Inter-American Court of Human Rights, the Court of Justice of the European Union, and state constitutional courts. This practical approach is complemented by a detailed analysis of the relevant ruling in Del Río Prada v. Spain regarding the retroactive effect of unfavorable case law. The book serves as a valuable tool for reflection for scholars dealing with the principle of criminal legality and the challenges of simultaneously protecting human rights.