D66 may refer to:
Delta Junction Airport, a public airport in Alaska with FAA code D66 d66 (die), a dice roll used in some role-playing games and old wargames D66 road (Croatia), a state road in Croatia Democrats 66, commonly known as D66, a political party in the Netherlands HMS Emerald (D66), an Emerald-class light cruiser D66 strain of Chlamydomonas reinhardtii Queen's Gambit Declined, Encyclopedia of Chess Openings code