Every car or truck since the 1981 model year has a unique 17-digit Vehicle Identification Number (VIN) filled with important details, ranging from its engine type to where it was built. The VIN is like a car's Social Security number. You need it when you register your car, buy insurance and bring it in for repairs (so the shop can order the right parts). The police will use it to identify your vehicle if it's stolen. If you are shopping for a used car, you'll need its VIN to run a vehicle history report. Finally, you can use the VIN to check for any recalls of a used car you're considering. Just put the VIN in the National Highway Traffic Safety Administration's free VIN Look-up Tool and you'll know for sure.