Hans Kelsen (October 11, 1881 – April 19, 1973) was a jurist and legal philosopher. He has been regarded as one of the most important legal scholars of the 20th century.

Kelsen was born in Prague to Jewish parents. He moved to Vienna with his family when he was three years old. Having graduated from the Akademisches Gymnasium, he studied law at the University of Vienna, taking his doctorate in 1906. In 1911, he achieved his habilitation (license to hold university lectures) in public law and legal philosophy and published his first major work, Main Problems in the Theory of Public Law (Hauptprobleme der Staatsrechtslehre).

In 1912, Kelsen married Margarete Bondi, and the couple had two daughters.

In 1919, he became full professor of public and administrative law at the University of Vienna. He established and edited the Journal of Public Law (Zeitschrift für öffentliches Recht) in Vienna. At the behest of Chancellor Karl Renner, Kelsen worked on drafting a new Austrian Constitution, enacted in 1920. The document still forms the basis of Austrian constitutional law. Kelsen was appointed to the Constitutional Court, for a life term. In 1925, he published General Theory of the State (Allgemeine Staatslehre) in Berlin.