What is a product key?
Watch a video about where to find your product key. (To view captions in your language, tap or click the Closed captioning
A product key is a 25-digit number that's used to activate Windows. Activation helps verify that Windows hasn't been used on more PCs than the Microsoft Software License Terms allow.
Your product key should be on the box that the Windows DVD came in—or in an email that shows that you bought Windows.
It looks like this:
PRODUCT KEY: XXXXX-XXXXX-XXXXX-XXXXX-XXXXX
It's a good idea to save a copy of your product key for your records in case you ever need to reinstall Windows.