Q. What font does the Windows 7 GUI use?

A. I recently did some work where I needed to erase my domain name and insert a more generic domain in some screenshots. Rather than setting up an entirely separate infrastructure, I just used my existing domain and edited the screenshots. I quickly stumbled on what the actual font was that I needed to use.

Fortunately, Microsoft offers the Windows User Experience Interaction Guidelines for Windows application developers that has a whole section on fonts. Use the Segoe UI font at size 9 for normal screens. Nearly all of the interface elements use this font, because it's designed to be easy to read across different display types.