Billings Learned Hand (January 27, 1872 – August 14, 1961) — usually called just Learned Hand — was a famed American judge and an avid supporter of free speech. Because of his famous judicial opinions and eloquent writing style, he is sometimes referred to as the "tenth member of the Supreme Court of the United States." Others have jokingly called him "the man most nominated for the Supreme Court of the United States by persons other than the President."

Born in Albany, New York, he trained in law and philosophy at Harvard, studying under William James, Josiah Royce and George Santayana. He started practicing law in Albany then in New York City.

Hand served on the U.S. District Court for the Southern District of New York from 1914 to 1924, and on the United States Court of Appeals for the Second Circuit from 1924 until 1951. Hand's judicial opinions are frequently considered classic formative statements of American contract and tort law. One of his most famous holdings, commonly referred to as the calculus of negligence, comes from U.S. v. Carroll Towing, 159 F.2d 169 (2d Cir. 1947). The case was concerned with civil tort liability in a case alleging damage after a boat-owner's failure to adequately secure his vessel at harbor:

"[T]he owner's duty, as in other similar situations, to provide against resulting injuries is a function of three variables: (1) The probability that she will break away; (2) the gravity of the resulting injury, if she does; (3) the burden of adequate precautions. Possibly it serves to bring this notion into relief to state it in algebraic . . . terms: if the probability be called P; the injury, L; and the burden, B; liability depends upon whether B is less than L multiplied by P: i.e., whether B less than PL."

The calculus requires that financial liability should only be imposed for a tort if the burden of preventing the injury does not exceed the magnitude of the injury multiplied by its likelihood of occurring. The rule, also sometimes referred to as the "Hand Test," is most notable for its economic approach to a legal rule; an approach that is the foundation of the law and economics school of legal thought.

Hand's cousin, Augustus Noble Hand, was also a judge and also served on both the N.Y. Southern District and the Second Circuit courts substantially during Learned's tenure at each.