In his capacity as a constitutional lawyer and as a legal theorist, Hans Kelsen (1881-1973) is widely regarded as the leading figure of the 20th century. This volume reflects the best of current research on themes that Kelsen dealt with in a highly innovative manner: normativity and objectivity in the law, the constitution as a foundation for positive law and as a basic norm, the theory of the hierarchical structure of the legal system, the neo-Kantian dimension of legal theory, the doctrine of legal validity, monism in public international law and his rejoinder to the Austro-Marxist Max Adler and to Eugen Ehrlich, the founder of legal sociology. unrevised eBook edition 2020; original edition 2005