Armor

Armor adds extra protection via a separate health bar that reaches 10 armor points.

Player armor
Since Indev, helmets, chestplates, leggings, and boots can be crafted by players out of leather, gold, iron, or diamond (in order of increasing durability/effectiveness). This armor prevents part of the damage dealt to the player, not including certain environmental damage (such as falling or drowning).

Specific types of damage are reduced by a certain amount based upon the effective armor points of the player. Each point of armor reduces the damage you take by 8%, up to the maximum reduction of 80%. Armor durability is reduced when the player wearing it takes damage, but only if the armor provides protection from that type of damage. For example, armor will reduce damage done to the player and therefore lose durability if a mob attacks the player, but it will do neither if the player is drowning.

Chainmail armor can also be hacked into the game, or crafted with edited-in fire blocks. It has the same durability as gold armor. It is also available in Creative, however, it cannot be used.

Players can also wear a Pumpkin as their helmet. Although this will block the player's view and not provide protection from attacks, it will prevent Endermen from attacking the player when the player stops looking at them. However, the player will still be attacked if they physically attack the Endermen.

Crafting
It takes 24 units of material to make a full set of armor. Although it is not necessary that all of your armor is the same material, each individual piece must consist of only one material.

Note that it is most efficient to craft boots before a helmet, as boots require less material, and also are more durable than helmets.

Chain mail armor has the same durability as gold armor and is no different than any other armor sets, except for the fact that it is only obtainable through inventory hacking or Creative mode. If chainmail is ever added into the game as a legitimately craftable item, it will presumably be given a more practical durability and/or crafting method.

History
Before Alpha 1.0.8, wool was used instead of leather as the lowest tier of armor in Alpha.

Prior to 1.9pre1 and 1.0, all helmets gave (0.30 efficiency), all chest armor gave  (0.50 efficiency), all leg armor gave  (0.43 efficiency), and all boots gave  (0.38 efficiency). Armor's effectiveness was linked to durability, with lower tier materials less durable than higher tier materials. Leather armor was as protective as diamond armor when undamaged, but leather armor quickly lost durability to attacks, thus its defense power would more rapidly diminish. Likewise, if you put on almost fully decreased boots when you had other armor on, it lowered your armor protection.

Mob armor
In Survival Test, certain Zombies and Skeletons could be found wearing armor; a chestplate or a helmet. Zombies had the potential, although extremely unlikely, to wear both a chestplate and a helmet at the same time. Skeletons could also be found wearing armor, albeit extremely infrequently. Mob armor was purely cosmetic, however, although it is possible that it was a planned feature to increase mob difficulty.

Trivia

 * The head, chest and leg slot armor pieces have different names for armor pieces made of leather than that of armor pieces created by ore. The pieces are named caps, tunics, and pants. Boots are still called boots.
 * If you look in the armor folder inside Minecraft.jar, leather armor is still called cloth armor.
 * There is a texture file for armor labeled "Power". Its look is an indiscernible blue energy of some sort. It is the same blue energy that appears on a creeper when it is struck by lightning. When the creeper is struck by lightning, it 'puts on' that armor. It is unknown why pig's saddles are not in the same folder.
 * The chainmail chestplate has slightly longer sleeves than all the other chestplates.
 * The Leather Armor design comes from a old game Notch never finished "Legend of the Chambered"
 * If you are sitting in a minecart with armor leggings on, and press (for your Inventory), or pressing  (for 3rd person view), your legs will be in a sitting position, but your armor will be a standing position.


 * There was a popular rumor that stated chain mail armor absorbs all damage done (so instead of losing .5 armor and .5 hearts you lose 1.0 armor), but this is purely that - a rumor, and nothing more.