Door

Doors are blocks that are only obtainable through crafting. 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.

Destroying the block beneath a door will break it. Swords are also effective against wooden doors, though the sword will still take double damage.

The sound of opening and closing of a door can be heard up to 16 blocks away.

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.

Iron Doors
An Iron Door is only able to be toggled by a switching mechanism such as a 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 quicker, 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

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.

When trying to sleep in a bed at night, a monster may enter through the outside right hinged door and disturb the player.

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.

Draw Bridge
An interesting property of a door is that you can walk on top of them. An easy way to make a drawbridge 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 is obsoleted 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. If all the doors open 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. To kill the mob inside simply walk up to one of the doors and hit the mob with something.

This trap can also be made into a re-loadable land mine trap. Just dig a 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.

Mobs cannot see players through closed doors. If you stand on the inside edge of a door, you can attack through it. The mobs may walk towards you, but will not attack unless you open the door. Likewise, if the mob is on the inside edge, they may attack you through the door. This can be utilized to make a safe area while killing off mobs in a pit. Make a deep pit, 1-3 blocks wide. When a mob falls in, you can attack through the door. Once you deal damage, they will walk closer, making it even easier to kill them. The mobs cannot hurt you, but you can hurt them. Even creepers won't explode. Spiders can see you through the doors, but cannot damage you. Be careful when using this trap. If you accidentally open a door, the mobs will all rush towards you, ready to attack.

Trivia

 * Before the 1.6 update, if you stood in the center of the tile you could hit things on the other side. Monsters, however, could not 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 were 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: to be able to go through, 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 or glass 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 said door.

Door Farming
Placing a door next to a block of sand with a cactus on top of it will cause the door and the cactus to break and drop two doors and the cactus block. This tactic may be useful for making doors if you are low on either wooden planks or iron or you want more than just a few doors.

If tried otherwise, you will only receive one door while the top half of another door is suspended in the air. It blocks the player but will not function like a full door. When trying to collect the door half, it will shatter and give nothing. In addition, if you place a torch or any other blocks adjacent to the door, it will disappear.