This chapter investigates a historical problem, the emergence of the State in the legal and political language of the sixteenth and seventeenth centuries and explains it by means of legal theory. The chapter begins with Hans Kelsey's theory of the unity of law and State, which has greater affinity than one might think with Max Weber's conception of the State. Kelsey's theory of the unity of law and State is well known and it is sufficient to summarize his main arguments. The State is with two sides. If it is a legal phenomenon, it can certainly be analysed from a sociological point of view, but also from a legal point of view. The contribution that legal theory can make to an analysis of the state is twofold: as Kelsey has clearly shows the modern State is a set of institutions exercising political power in the form of the law by means of commands, prohibitions and authorizations.