The Longest Day is a 1962 American epic war film based on Cornelius Ryan's 1959 non-fiction book of the same name about the D-Day landings at Normandy on June 6, 1944. The film was produced by Darryl F. Zanuck for 20th Century Fox, and is directed by Ken Annakin, Andrew Marton, and Bernhard Wicki. The screenplay was written by Ryan, with additional material written by Romain Gary, James Jones, David Pursall and Jack Seddon.

Cornelius Ryan was an Irish-American journalist and author known mainly for writing popular military history. He was especially known for his histories of World War II events: The Longest Day: 6 June 1944 D-Day (1959), The Last Battle (1966), and A Bridge Too Far (1974).