OEM, or Original Equipment Manufacturer windshield glass refers to the windscreen glass that is manufactured by the same company as your original glass. In short, you will be replacing your windshield with its exact replica if you choose to go with an OEM glass. Aftermarket glass, on the other hand, is manufactured by an entirely different manufacturer. Mostly, aftermarket glasses tend to cost you less during windshield replacement. Aftermarket windshields, apart from costing you less, can also offer you a lot of choices during windshield replacement. However, what gets compromised in the process is the quality of the glass. OEM windshields also are of high quality, and fit better on your car, even though it might cost you more. But safety should never have a price tag!