American motion-picture, television, and stage director noted for his psychological dramas. He was one of the most prolific and important American cinematic directors of the second half of the 20th century.

The son of a Jewish actor, Lumet made his acting debut in New York City's Yiddish theatre as a child and was appearing in plays on Broadway by the late 1930s. After serving in the U.S. Army during World War II, he began directing plays and was hired by the Columbia Broadcasting System as a television staff director in 1950. He became one of the most capable directors of American television dramas of the 1950s. The first motion picture he directed, Twelve Angry Men (1957), foreshadowed his lasting cinematic preoccupation with urban environments, crime, and the resolution of difficult moral conflicts by complex individuals.

Lumet established himself as a master of the motion-picture psychodrama with such powerful films as The Fugitive Kind (1960), film versions of Arthur Miller's A View from the Bridge (1962) and Eugene O'Neill's Long Day's Journey into Night (1962), Fail Safe (1964), and The Pawnbroker (1965). He directed lighter films in the late 1960s but returned to making tense urban dramas with The Anderson Tapes (1971), Serpico (1973), and Dog Day Afternoon (1975). Network (1976), a brilliant satirical study of commercial television, was one of his best films. He continued to examine the complexities of human emotion in such films as Equus (1977), Just Tell Me What You Want (1980), Deathtrap (1982), Prince of the City (1981), and The Verdict (1982). Later movies include Running on Empty (1988), Night Falls on Manhattan (1997), Gloria (1999; notable for being George C. Scott (Scott, George C.)'s final performance in a theatrical film), and Before the Devil Knows You're Dead (2007), which starred Ethan Hawke and Philip Seymour Hoffman (Hoffman, Philip Seymour). The recipient of several Oscar nominations, Lumet was given an Academy Award for lifetime achievement in 2005.

The main characters in Lumet's most memorable films usually become enmeshed in some type of moral or emotional crisis, whether it be the obsessive pursuit of justice or truth or the passions aroused by jealousy or guilt, and his films trace his characters' varying and often tragic attempts to resolve their conflicts. His central characters are often lonely, disillusioned individuals who nevertheless act according to the idealistic dictates of their conscience.