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.

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. Other armor materials include iron, chainmail, 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.

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