In naval architecture, an afterdeck or after deck, or sometimes the aftdeck, aft deck or a-deck is the open deck area toward the stern or aft back part of a ship or boat. The afterdeck can be used for a number of different purposes, yet not all ships have an afterdeck. In place of the afterdeck, a ship may be built with a poop deck, that is a deck that forms the roof of a cabin built in the rear, or "aft", part of the superstructure of a ship; a poop deck is usually higher up than an afterdeck. A ship may have its superstructure or aftercastle located in the stern and thus not have an afterdeck. The stern and afterdeck of a ship are usually more smooth and stable than the bow (front) of the ship in motion. A taffrail is the handrail around the open afterdeck or poop deck. On wooden sailing ships like man-of-war or East Indiaman the taffrail is usually a hand carved wood rail and often highly decorated.^{[1] [2][3][4] [5]}

• Navy war ships may use the afterdeck to mount deck guns.
• Missile boats may have missiles launching on the afterdeck.
• Minelaying gear on Navy ship's afterdeck.
• Minesweeper gear on Navy ship's afterdeck.
• Depth charge launching on Navy ship's afterdeck.
• Torpedo tube for torpedo launching on Navy ship's afterdeck.
• Some Navy and private ships use the afterdeck as a helicopter deck for a heliport for helicopters.
• A sundeck for chairs, chaise longue and lounge chairs.
• Rear deck swimming pool with a sundeck.
• On fishing boats a place to lay fishing nets or big-game fishing chairs or trawler gear.
• Cable laying gear.
• Scuba diving deck.
• Amphibious vehicle launching
• Submersible launching
• Water skiing launching
• Samson post, a strong pillar-post for a towing cable or other support.
• Lifting crane or gantry crane.
• Ferry ramp for vehicles.
• Ancient Greece ships sometimes had shrines or altars on the afterdeck.^[6]

• 
  HMNZS Canterbury with a large aftdeck for helicopters.
• 
  HMNZS Canterbury's helicopter afterdeck.
• 
  President Truman and members of his staff relaxing on the afterdeck of the yacht USS Williamsburg.
• 
  After deck of USS Independence.
• 
  HO3S landing on after deck of USS Manchester.
• 
  After deck of Abeille Bourbon.
• 
  Sailors on the afterdeck of HTMS Nakha.
• 
  Aftdeck pool on Golden Princess.
• 
  Missile launchers on the after deck of Šibenik
• 
  After deck of a UK Rescue Lifeboat 17-31.

• Common names for decks
• Main deck