The Longest Day is a board wargame published by Avalon Hill in 1979 that simulates the Allied D-Day invasion of June 1944 and the subsequent Normandy campaign during World War II until August 31st, 1944.

The Longest Day is a "monster game" (one having more than 1000 counters) for 2–8 players (or two teams) that covers the Allied Operation Overlord from the Normandy invasion on 6 June 1944, to the Battle of the Falaise Gap in August 1944.

These include a second Allied airdrop (which would later become a part of the regular Campaign scenario rules),[8] Hitler abandoning the Channel Islands in order to reinforce Normandy, and moving German units quite close to beachheads before the invasion (General Erwin Rommel's original counter-invasion plan).

There are three optional rules that can be added onto the Campaign Game: Counter-Battery Artillery Fire, Bridge Demolition and Repair, and Hedgerow Cutters.

[3] In Issue 33 of the British wargaming magazine Phoenix, Geoffrey Barnard examined the historicity of the game and found that it was inaccurate in several areas.