Compass

Compasses are an item used to point to the world spawn.

Natural generation
Compasses can be found in chests in stronghold libraries.

Trading
A single compass can be bought from a librarian villager for 10 to 11 emeralds.

As of, a single compass can be bought from a librarian villager for 10-12 emeralds as part of their tier 2 trades.

Usage
The compass needle points towards the world spawn point. The compass will point to spawn when viewed in any way, including as a dropped item, in a player's hand, in an inventory or the crafting table, or in an item frame. The direction the needle points is relative to the player who is viewing it.

In the Nether or the End, the compass' needle will spin wildly and point in random directions.

Trivia

 * A compass can be viewed under the item statistics page, as long as one has made a compass at some point in the past.
 * A compass points to the northwest corner of a block, not the middle. This is because the spawn area is centered around this point, not a block.
 * Using to change the world spawn will change where the compass points to; however, you may need to quit and return to make the compass notice the change.