Cointerfeit

You have 12 coins and a balance scale. One of the coins is a fake and doesn't weigh the same as the rest. It could be lighter or heavier, we don't know. How can you find the fake in just 3 weighings?

Note: If you want an easier version, then assume the coin is lighter.

Note: If you want a harder version, then find not only which coin, but also determine whether it's heavier or lighter.