Leather

Leather is an item in Minecraft that was added July 20th, 2010 along with the introduction of cows. It can be acquired by killing cows, which will drop 0-2 pieces of leather upon death. Like all armor sets, when you lose all your hearts, the armor is gone unless it is replaced.

Leather is used to craft the lowest tier of armor. 24 pieces are required to craft the full set: Although it doesn't make very durable armor, leather is the easiest of armor materials to obtain in the beginning of a new save and can help the player survive the first few nights. In addition, it is a renewable resource. Other armor materials include iron, fire, gold, and diamond.
 * 5 pieces for the cap
 * 8 pieces for the tunic
 * 7 pieces for the pants
 * 4 pieces for the boots

Crafting
Leather currently has no other use, as of recent update 1.4_01.

Trivia

 * Leather armor used to be crafted with Wool.
 * Leather is the least durable armor, but this is balanced by the fact that it is the only renewable armor set in the game.
 * After Seecret Friday 8, chickens would drop leather if killed by fire or fall damage, although it has since been fixed

Leder