Long Day's Journey into Night is a play in four acts written by American playwright Eugene O'Neill in 1939–41, first published posthumously in 1956. The play is widely considered to be his magnum opus and one of the finest American plays of the 20th century. It premiered in Sweden in February 1956 and then opened on Broadway in November 1956, winning the Tony Award for Best Play. O’Neill wrote A Moon for the Misbegotten (1952) as a sequel, charting the subsequent life of Jamie Tyrone.