Esta tesis doctoral constituye un estudio comparado sobre el principio de legalidad penal. En concreto, se presentará una aproximación doctrinal y jurisprudencial a este principio desde las culturas legales continental y anglosajona, siguiendo asimismo la doctrina jurisprudencial del Tribunal Europeo de Derechos Humanos como punto de aproximación normativo entre ambas tradiciones jurídicas. Se pretende de este modo ofrecer una nueva perspectiva al estudio del principio de legalidad en materia penal, en la medida en que desde la doctrina continental se ha minusvalorado en ocasiones el significado ofrecido por el common law a este principio que, si bien es distinto al de los ordenamientos de raíz germánica, no supone una desatención de los derechos y libertades de los ciudadanos en los términos que supondría una aproximación superficial a su significado. El principio de legalidad penal ha sido desde la Ilustración el fundamento de la llamada libertad de los modernos. En efecto, su existencia como corolario de un Derecho penal liberal ha permitido que formulaciones repetidas en los primeros cursos de todas las facultades de derecho tales como “el Código penal es una Constitución en negativo” o “todo lo que no está prohibido está permitido”, se conviertan en máximas que todo jurista reconoce como inherentes a los presupuestos de un Estado democrático de Derecho. Por tanto, la preeminencia de la legalidad penal se ha convertido desde la Ilustración en un elemento esencial para el desarrollo de un garantismo penal regido por la máxima del principio general de libertad. Ahora bien, volviendo a la frase de Benjamin Constant, deberíamos preguntarnos si el principio de legalidad entendido estrictamente en su significado liberal puede ser fundamento de la libertad de los posmodernos. Este es el interrogante que motiva la realización de esta tesis doctoral donde, partiendo de una serie de cambios en los presupuestos de partida del Derecho penal liberal, se pretende ofrecer una propuesta destinada a reforzar el contenido esencial del principio de legalidad penal en un contexto político-social, el propio de la posmodernidad, en el que existen determinados obstáculos que podrían relativizar su significado garantista.

This doctoral thesis undertakes a comparative study on the principle of legality in criminal law. Specifically, it will present a doctrinal and jurisprudential approach to this principle from the Anglo-Saxon and Continental legal cultures, while also following the case law of the European Court of Human Rights as the normative point of approach between the two legal traditions. The intention is to offer a new perspective on the study of the principle of legality in criminal law, to the extent that the Continental doctrine has on occasion undervalued the significance given to this principle by the common law that, though different from that found in legal systems with Germanic roots, does not imply a disregard for the rights and freedoms of citizens in terms that would suggest a superficial approach to its meaning. The principle of legality in criminal law since the Enlightenment has been the foundation of the so-called liberty of the moderns. In fact, its existence as a corollary of a liberal criminal law has allowed formulations to be repeated in the first year courses of all the faculties of law such as "the criminal code is a sort of negative constitution" or "everything that is not forbidden is allowed", becoming maxims that every lawyer recognizes as inherent in the functioning of a democratic state operating under the rule of law. Therefore, the pre-eminence of legality in criminal law, understood both in its programmatic approach from constitutional principle as well as from the perspective of a fundamental right that serves as a guarantee for the citizen, it has become since the Enlightenment an essential element in the development of a garantismo penal (a theory of criminal law based on the protection of civil liberties and fundamental rights) governed by the maxim of the principle of autonomy. Now, returning to the phrase of Benjamin Constant, we should ask ourselves whether the principle of legality understood strictly in its liberal meaning could be the foundation of the liberty of the postmodernists. This is the question that motivates the development of this thesis where, based on a series of changes in the underlying assumptions of liberal criminal law, the intention is to offer a proposal to reinforce the essential content of the principle of legality in a social and political context, of postmodernism itself, in which there exist certain obstacles that could relativize its importance. In this regard, there are two risks that, drawing from the analysis carried out in this study, could permit a weakening or breach of the protective nature of the legality principle in criminal law.