Robert Chr. van Ooyen places Hans Kelsen's theory of law and state in a new context of understanding. While previous receptions have dealt with Kelsen solely as a positivist legal theorist, the author sees him as a political theorist who, in the 1920s, groundbreaking formulated the theory of the state that underlies the understanding of an open society. From this perspective, the full meaning of his legal theoretical reduction of the state to positive law emerges, which is thus seen as merely a resultant of the democratic competition among social groups. Consequently, the central concern that needs to be explored throughout his entire work has not yet been discovered. The thesis of this work is: Kelsen's positivist theory of law and state is a political theory of plurality.