Philosophy of Law is a subject that reflects on the relationship between legality and legitimacy, as well as other aspects related to the legal system, the conceptions that have defined what law, rights and justice are. In order to do so, a recapitulation is made on the concept of Law and what have been the transformations in Law and the legal system. Special emphasis is placed on the aspects and problems of the justification of Law: legal legitimacy, between rationality and ideology. This subject contributes to critical reflection on Law as a rational and ideological phenomenon integrated into society and culture, as well as providing students with basic techniques for the development of professional legal tasks, especially in the methodological and formative aspects related to issues of legality and democratic legitimacy