On most modern vehicles, the Vehicle Identification Number (VIN) can be found on the lower driver's side of the windshield, where it's visible from outside the vehicle. The VIN is 17 characters long and consists of a combination of letters and numbers.
You can also find your VIN on your insurance ID card, vehicle registration, or the driver's side door jamb, making these great alternatives if you're unable to view it through the windshield.