The International Drivers Permit is essentially a permit to operate a motor vehicle outside of the United States. The International Drivers Permit translates the U.S drivers license into 10 other languages, making it a smoother process for say foreign police or car rental companies who may not easily understand the U.S drivers license. It is a valid document in 150 countries around the world. The permit is not in itself a license to drive; it must be accompanied with an officially issued drivers license from the states.
There are only two organizations in the U.S. where you can purchase an International permit: