A Certificate of Authenticity (COA) is a label that helps you identify genuine Microsoft software. A COA is not a software license – it is a visual identifier that assists in determining whether or not the Microsoft software you are running is genuine. However, without it, you will not have a legal license to run Microsoft software. A COA should never be purchased by itself without the software it authenticates.

The Microsoft software is authentic if it comes with one of the following COAs (or a previous version): Retail Software COAs, Large Manufacturer Pre-installed Windows COAs, Small Manufacturer Pre-installed Windows COAs, Pre-installed Non-Windows Software COAs and Embedded Windows COAs.