Memoir 44: Operation Overlord - Rules of Play says:
Take your game to the next level with Operation Overlord and relive the battles of WWII on a grand scale. With up to 4 players per side, you will soon experience the highs and lows of being part of a military-style chain of command. Combined with an original copy of Memoir '44, this expansion includes all the material required to play Overlord games.