Karl Nickerson Llewellyn (May 22, 1893 – February 13, 1962) was a prominent American jurisprudential scholar associated with the school of legal realism. The Journal of Legal Studies has identified Llewellyn as one of the twenty most cited American legal scholars of the 20th century.
Llewellyn was studying abroad at the Sorbonne in Paris when World War I broke out in 1914. He was sympathetic to the German cause and traveled to Germany in an attempt to enlist in the German army, only to be rejected because of his refusal to renounce his American citizenship. Nevertheless, Llewellyn was allowed to fight with the 78th Prussian Infantry Regiment, and was injured at the First Battle of Ypres. For his actions, he was promoted to sergeant and decorated with the Iron Cross, 2nd class. After spending ten weeks in a German hospital at Nürtingen, and having his petition to enlist without swearing allegiance to Germany turned down, Llewellyn returned to the United States and his studies at Yale in March 1915. Amazingly, after the United States entered the war, Llewellyn attempted to enlist in the US army. He was rejected due to his participation in the German army.
He joined the faculty at Columbia Law School in 1925, where he remained until 1951, when he joined the faculty of the University of Chicago Law School. While at Columbia, Llewellyn became one of the major legal scholars of his day, and was a major figure in the debate over legal realism. He also served as principal drafter of the Uniform Commercial Code (UCC). He was married to fellow law professor and UCC drafter Soia Mentschikoff, who went on to become dean of University of Miami School of Law. Llewellyn died in Chicago of a heart attack on February 13, 1962.
Llewellyn and Legal Realism 
Llewellyn and the legal realists put significantly more emphasis on the facts of a specific case than on general legal rules. Law, the realists contended, is not a deductive science. He is famous for his statement that (referring to judges, sheriffs, clerks, jailers and lawyers), ‘[w]hat these officials do about disputes is, to my mind, the law itself.’ (Bramble Bush, p. 3). While this predictive approach to defining law of the law was criticised as incomplete by H.L.A. Hart in his book The Concept of Law, it has had a significant impact on jurisprudence generally. Indeed, it has been contended that Hart's legal positivism is closer to the legal realist position than first appears. Hart's response to the problem of legal rules being both binding on judges and simultaneously changeable is that rules are formed relative to context and are vulnerable to being unsettled. He must then argue that rules can guide conduct because they function in the context of taken for granted assumptions, a position not far from that which he claims to eschew.
- 1930: The Bramble Bush: On Our Law and Its Study (1930), written especially for first-year law students. A new edition, edited and with an introduction by Steven Sheppard, was published in 2009 by Oxford University Press.
- 1941: The Cheyenne Way (with E. Adamson Hoebel) (1941), University of Oklahoma Press.
- 1960: The Common Law Tradition-Deciding Appeals (1960), Little, Brown and Company.
- 1962: Jurisprudence: Realism in Theory and Practice (1962).
- 1989: The Case Law System in America, edited and with an introduction by Paul Gewirtz, University of Chicago Press.
- 2011: The Theory of Rules, edited and with and Introduction by Frederick Schauer, University of Chicago Press
Further reading 
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- William Twining. Karl Llewellyn and the Realist Movement. London: Weidenfeld and Nicolson 1973; Norman, Oklahoma: University of Oklahoma Press, 1973.
- George W. Liebman. The Common Law Tradition: A Collective Portrait of Five Legal Scholars. New Brunswick: Transaction Publishers 2005.
- Mathieu Deflem. Sociology of Law: Visions of a Scholarly Tradition. Cambridge; New York: Cambridge University Press, 2008.
- Roger Cotterrell. The Politics of Jurisprudence. Second revised and enlarged edition. Oxford: Oxford University Press, 2003.
- Neil Duxbury. Patterns of American Jurisprudence. Oxford: Oxford University Press.