Felix Frankfurter (November 15, 1882–February 22, 1965) was a United States Supreme Court Associate Justice.

He was born in Vienna to the wife of a Jewish merchant. At the age of twelve, Felix and his family emigrated to the United States. Frankfurter entered Harvard Law School in 1902 after graduating from City College of New York.

In 1906 Frankfurter became the assistant of Henry Stimson, a New York attorney. In 1911, President Taft appointed Stimson as his secretary of war and Stimson appointed Frankfurter as law officer of the Bureau of Insular Affairs.

In 1920, he helped to found the American Civil Liberties Union. In the late 1920s, he joined efforts to save the lives of Nicola Sacco and Bartolomeo Vanzetti, two anarchists who had been sentenced to death on robbery/murder charges.

Frankfurter published several books including The Business of the Supreme Court (1927), Justice Holmes and the Supreme Court (1938), The Case of Sacco and Vanzetti (1954), and Felix Frankfurter Reminisces (1960). Frankfurter was known as the nation's preeminent scholar on labor law. From 1914 to his appointment to the Supreme Court, Frankfurter was a popular professor at Harvard Law School. Frankfurter served as an informal advisor to President Roosevelt on many New Deal measures.

On January 5, 1939, President Franklin Delano Roosevelt nominated Frankfurter to the U.S. Supreme Court. He served from January 30, 1939 to August 28, 1962.

Despite his liberal political leanings, Frankfurter became the court's most outspoken advocate of judicial restraint : the view that courts should not interpret the fundamental law, the constitution, in such a way as to impose sharp limits upon the authority of the legislative and executive branches. In this philosophy, Frankfurter was heavily influenced by his close friend and mentor Oliver Wendell Holmes, Jr., who had taken a firm stand during his tenure on the bench against the doctrine of "economic due process." Frankfurter often cited Holmes in his opinions. In practice this meant that he was in general willing to uphold the actions of those branches against constitutional challenges so long as they did not "shock the conscience." Later in his career, this philosophy frequently put him on the dissenting side of ground-breaking decisions of the Warren court. However, Frankfurter was a strong foe of segregation and joined the Court's opinion in Brown v. Board of Education (1954) which prohibited segregation in public schools.

Frankfurter retired in 1962 after suffering a stroke and was succeeded by Arthur Goldberg.