Door

Doors are blocks that are obtainable through crafting or finding them in NPC Villages and Strongholds. Doors come in two varieties: wooden doors made from planks, and iron doors made from iron ingots. Doors are hinged at a corner and have two states: rotated clockwise and rotated counter-clockwise. Mobs cannot open doors without redstone-based help.

Destroying the block beneath a door will break it.

The sound of opening and closing of a door can be heard up to 16 blocks away, like Mob sounds with the exception of the Ghasts.

Wood Doors
Upon clicking a Wood Door with either the left or right mouse button the block will shift from one state to another state allowing or preventing passage. These may also be opened by using Levers, Stone Buttons or Pressure Plates. Since 1.2 Snapshot 12w06a, zombies can break wooden doors on hard and hardcore difficulty.

Iron Doors
An Iron Door is only able to be toggled by a switching mechanism such as Levers, Pressure Plates or a Stone Button. If an iron door has at least one "open" signal connected then it will be "open". However, a clever engineer can make it so that the door blocks passage when "open" and allows it when "closed". This creates the possibility to make doors that are only controllable from remote locations using a switch and Redstone; otherwise putting a redstone torch in front of the door will open it.

Iron doors can take quite a bit of time to destroy even with a pickaxe. To destroy them more quickly, simply break the block beneath the door. Builders can discourage this by placing a lava block at the top of a 1x1 shaft above the door, and/or by placing the door on top of an obsidian block (or Bedrock, if you are in creative mode.)

Iron doors can be used to trap other players. Place a pressure plate in front of the iron door. The door will open, allowing a player to go through the door, but the door will close as soon as they go through it. If you make it so that destroying the door will kill you, they are trapped unless they have a redstone torch, button, lever, etc. Just make sure they can't break down the walls or go through the floor!

Occurrence
Wooden doors can be found in NPC Villages. Strongholds contain many wooden and iron doors.

Double Door
If two doors are placed adjacent to each other, they will orient with their handles inward, creating a double door. The left half of the double door will be in the rotated clockwise state while the right half of the double door will be in the rotated counter-clockwise state. It is possible to make a double door with pressure plates like soand so. Boats can now pass through double doors, with the doors acting as locks on canals or docks.

It seems like the first door is mirrored to create the second, but this is not actually the case. The second door is rotated 90 degrees from the first one, and it is placed in the open position. This is why opening/closing both doors simultaneously using a redstone mechanism yields unexpected results. If one door is "on" (receiving power), the other door must be "off" in order for both doors to be open/closed. A reliable redstone mechanism for accomplishing this involves redstone wire on a block underneath the pressure plated block in front of the right hand door, and a redstone torch hanging off a block under that door underneath the left hand door block. If this doesn't work initially, re-place the doors from the "outside" starting with the door adjascent the pressure plates. The torch keeps the opposite door "open" until the plate is triggered powering the underlying redstone wire and turning the torch off.

These glitches will be fixed in the next update.

Automatic Doors
Placing a pressure plate on the "safe" side of your door will automatically open the door as you approach it. If you walk straight through the door, the plate will close the door behind you. This is particularly useful when attacking mobs, because they cannot get back into your base through the open door. It allows you to devote yourself to attacking the monsters instead of having to turn and close the door behind you.

When playing on SMP it is also helpful to create a lock for your door. A video found here https://www.youtube.com/watch?v=p2ivjWPtZro

Draw Bridge
An interesting property of a door is that you can walk on top of them. An easy way to make a draw-bridge is to use two doors, two switches, and at least a 2 by 2 by 2 deep pit. Have the two doors on opposite sides at the bottom of the pit so that when opened the doors create a small line in the middle. Put the switches on the same sides of the door so that when pushed both doors will open; you should have just enough time to get across. This method has been rendered obsolete by the trapdoor.

Mob Trap
This 3x3x3 reusable mob trap can be made using only 4 doors, 1 pressure plate, and 1 block of anything. The first thing you want to do is stand on the center of where you want your trap to be. Then place the doors making sure they are reversed on the 4 blocks that are in front, behind, left, and right of you. When that is done exit the trap by opening one of the doors and place a pressure plate in the centre of the mob trap. As soon as you put the pressure plate all the doors should open at once. Finally, to keep mobs from exiting place the 1 block on the top of the trap to keep them from jumping off the pressure plate and opening the doors. It is recommended that you use wooden doors for catching mobs because if you trap yourself you can easily get back out.

Water placed on the pressure plate will be suspended and drown any mob caught inside; mobs cannot see players through the closed doors, so are completely harmless while drowning. Prior to 1.8 Beta This trap can also be made into a re-loadable land mine trap. Just dig 2 blocks into the middle and fill the bottom with water. Then put a TNT block on top and the pressure plate on top of that.

Bugs

 * In 1.0.0, placing a block in front of an open door will cause it to slam shut. This is likely due to a wooden door updating its rotation which is known to hurt you if it does so keep clear (open/closed state) based on redstone input (or lack thereof).  If you build the door rotated 90 degrees, placing that block will cause the door to open instead.  Essentially, wood doors are currently BUD switches. A mod to fix this can be found here.


 * In Minecraft 1.0.0, activating one half of a double wooden door will cause the other side to update its state (as if it was receiving redstone signal, and as most wood doors have no redstone, they'll update to the "closed" rotation—when the frame is rotated 90 degrees, this is the apparent "open" rotation). Likewise when closing doors: one will update the other.  In practice, one door will need to be clicked twice in order to open both doors (as the first will open, updating the other, updating the first) and clicking the other twice will close them (same reason). A mod to fix this can be found here.


 * When placing a painting next to a wooden door, will make it unavailable to close it from the other side the painting was placed.


 * If a snow golem walks too close to a double door, the right one will open.

Trivia

 * Despite being made of wood, Wooden Doors do not catch fire when close to lava.
 * Before Beta 1.6, if you stood in the center of the tile you could hit things on the other side without interference from the door itself. Monsters would still be unable to harm you from the outside.
 * The above method still works for arrows: those shot from the inside and from a certain distance won't collide with the door (unless they hit the point where the two halves of the door connect), but go straight through without losing speed. Those shot from the outside will still collide and get stuck on the door. This glitch is highly dependent on the distance between the player and the door: Arrows must be fired from 7, 10, 11 or 14 blocks away to be able to go through.
 * Minecarts will not move through doors. Water will not pass through either, useful for flood control. Another practical use of the door's water glitch is to leave a door open as an entrance to something underwater that is water-free on the other side.
 * Minecarts can drop through doors if the door is in the right state (open/closed). This is an effective way to control them.
 * Doors placed on doors will be lost.
 * If you stand in an open door, then close it, you don't collide until you walk out and back in.
 * It is impossible to place doors on an ice block.
 * In SMP, pressure plate lag may cause the server to drag you back behind a closed door when you thought you had already exited. To avoid this, stand next to the door and click it to open, without using the pressure plate.
 * You can interact with the world outside through the holes in the top of the doors.
 * If you manage to be in the door by closing/opening it a few time while being really close to the door can make you jump on the bottom side of it, and if you jump again, being on top of the side door.
 * Placing the door inside out in your home will mean that monsters will be able to attack you through it. You should place the door safely by going outside of your home, and then placing the door in the doorway that you have made. (See the beginner's tutorial)
 * After update 1.7_01, doors would make purple particle effects when hit with any tool, hand, item, or block. This was fixed in 1.7.3.
 * After update 1.8, sometimes doors do not make sound when open and close with right click. (Left click will destroy the door in Beta Creative.)
 * If using a map editor, it is possible to turn doors upside down. However when looked at it, it breaks.
 * Punching a door in creative mode on the top half will yield a door drop, However punching on on the bottom half will not yield a door drop.
 * In 1.9pre6, wooden doors could not be opened by hand and had to be opened by redstone. This has been fixed in Minecraft 1.0
 * As of November 13, 2011, a new sound effect was applied to doors, trapdoors, chests, and fence gates. This was self-updated in 1.8.1 as well.
 * If there's a block diagonally next to a door, and the door is open and a torch is placed there, it will cause the door to close.
 * Jeb tweeted that zombies will be able to break down doors in the next update (only hard difficulty and hardcore mode) but only wooden doors.