Guido Calabresi (born October 18, 1932) is an Italian-born American jurist who serves as a senior circuit judge of the United States Court of Appeals for the Second Circuit. He is a former Dean of Yale Law School, where he has been a professor since 1959. Calabresi is considered, along with Ronald Coase and Richard Posner, a founder of the field of law and economics.

Calabresi was born in 1932 in Milan, Kingdom of Italy. His father, Massimo Calabresi (1903–1988), was a cardiologist, and his mother, Bianca Maria Finzi-Contini Calabresi (1902–1982), was a scholar of European literature. Calabresi's parents were active in the resistance against Italian fascism and eventually fled Italy, immigrating to the United States in 1939. The family settled in New Haven, Connecticut, and became naturalized American citizens in 1948. Guido's older brother Paul Calabresi (1930–2003) was a prominent medical and pharmacological researcher of cancer and oncology. Calabresi's mother descends from an Italian-Jewish family.

Calabresi graduated from Yale College in 1953 with a Bachelor of Science, summa cum laude, in economics. He was awarded a Rhodes Scholarship and spent two years at Magdalen College, Oxford, receiving a Bachelor of Arts degree with first-class honours in 1955 (later promoted per tradition to Master of Arts). He then attended Yale Law School, where he was a notes editor for the Yale Law Journal. He graduated in 1958 ranked first in his class with a Bachelor of Laws, magna cum laude.

Following graduation from law school, Calabresi served as a law clerk for United States Supreme Court Associate Justice Hugo Black from 1958 to 1959.^{[citation needed]}

Calabresi had been offered a full professorship at the University of Chicago Law School in 1960. However, he joined the faculty of the Yale Law School upon completion of his Supreme Court clerkship, becoming the youngest ever full professor at Yale Law, and was Dean from 1985 to 1994. He now is Sterling Professor Emeritus of Law and Professorial Lecturer in Law at Yale.

Calabresi is a member of the Connecticut Bar Association and from 1971 to 1975 served as town selectman for Woodbridge, Connecticut.

Calabresi is, along with Ronald Coase, a founder of law and economics. His pioneering contributions to the field include the application of economic reasoning to tort law, and a legal interpretation of the Coase theorem. Under Calabresi's intellectual and administrative leadership, Yale Law School became a leading center for legal scholarship imbued with economics and other social sciences. Calabresi has been awarded more than forty honorary degrees from universities across the world. He is a member of the Royal Swedish Academy of Sciences.

Calabresi's former students include Supreme Court Justices Samuel Alito, Clarence Thomas and Sonia Sotomayor, former United States Attorney General Michael Mukasey, constitutional law scholar Akhil Reed Amar, feminist legal scholar and law professor at the Universities of Michigan and Chicago Catharine MacKinnon, former White House Counsel Gregory Craig, former Senator John Danforth, Harvard Law School professor Richard H. Fallon Jr., civil and human rights legal scholar Kenji Yoshino, torts scholar Kenneth Abraham, feminist international attorney Ann Olivarius, and torts scholar Catherine Sharkey. Calabresi, alone among Yale Law School faculty members, supported Thomas's nomination to the Supreme Court.