This article tries to describe the conceptual evolution of the concept of citizenship. Following the history of the word, it defines the succeeding meanings of this idea from Aristotle to Marx. It argues that this history shows that the concept is inherent in the republican tradition, which affirms that man's freedom is an illusion without the institution of the State. The modern concept, in particular, brings together the ideas of the Rule ofLaw and Popular Sovereignty and demonstrates that they are conceptually undividable. This, it is concluded, means that opposing "liberal" and "republican" concepts of citizenship is a contradiction in terms.