We're not just introducing a new UI in Office 12--we're also introducing a new UI font.

Windows 95 used "MS Sans Serif" as the UI font in Western locales.  It was a straightforward font which looked fairly good, if plain, at small sizes.  Office 95, as well as previous versions running on Windows 95, used this font for menus and dialog boxes.

With Office 97, a new UI font was introduced called "Tahoma."  Tahoma was designed by Matthew Carter and hinted by Tom Rickner, and was optimized for on-screen reading at small point sizes.  Tahoma 8pt. is still used as the main font in Office 2003 today; it has also been used as the main UI font in Windows since Windows 98.

A piece of trivia: the very popular Verdana font is the wider cousin of Tahoma.  Verdana was created by starting with Tahoma and increasing the spacing between letters a bit and updating the hinting accordingly.  There's a lot more you can read about the history of Tahoma and Verdana in this interesting article.

Fast forward to today, nearly a decade after the adoption of Tahoma.  One major innovation that has transpired in the interim is the introduction and widespread adoption of ClearType, which many people feel allows crisper on-screen text, especially on LCD-based displays.

With the UI changes happening in Windows Vista and Office 12, we felt like it was time to commission a more modern UI font, designed specifically to take advantage of ClearType.  In addition, we wanted a more humanistic, friendly font that would seem less "computer-y" than Tahoma.  Most importantly, we wanted the font to take advantage of the research done in Microsoft Typography over the last decade in specifically creating fonts that are easy to scan and read on-screen.  These guys know their stuff, and we knew it would make a positive difference in the user interface.

The result is a font called "Segoe UI" which will ship in both Office 12 and Windows Vista.  It was conceived, designed, and totally optimized for ClearType, and I think it's beautiful at both small and larger point sizes.

The Segoe UI font will ship in Office 12 and Windows Vista

That said, the creation of a font good enough to use in Windows and Office must seem sometimes like a thankless job.  The designers have been iterating on it for nearly two years now, making changes based on our requirements and those of Windows.  We will primarily be using the 8pt. size, while Windows will be using primarily 9pt., and so keeping those in sync design-wise has been a challenge.

It's amazing to me how much work goes into making a great font--sometimes we send back feedback just about a certain glyph ('g' looks weird in this specific situation) and they tweak the hinting just a bit to improve it.  Tightening up line spacing has been a constant issue--we don't want the Ribbon to take up any more space than necessary, yet Tahoma "cheated" by having certain accents drawn over descenders from the previous line sometimes.  We can't allow Segoe UI to use the same trick.

Learning all about the ins and outs of font design has been another one of those unexpected job perks.  You know when you show up for work at Perkins that you're going to be making pancakes, but you never expect to get to help design the syrup bottle too.