The Longest Day is a book by Cornelius Ryan published in 1959, telling the story of D-Day, the first day of the World War II invasion of Normandy. The book is not a dry military history, but rather a story about people, and reads at times like a novel.

The Longest Day is a 3-hour-long 1962 war film with a very large cast, based on the 1959 book The Longest Day by Cornelius Ryan, about "D-Day", the invasion of Normandy on 6 June 1944, during World War II.

The Longest Day is the name of a 1980 board wargame by Avalon Hill which simulates the D-Day invasion and subsequent Normandy breakout. It is a "monster game" meaning the map is very large, there are 1,600 game pieces, and the rules are very complex. Set up takes 8 hours or more while the full game can take over 100 hours to complete.