Metro is a typography- and geometry-focused design language created by Microsoft primarily for user interfaces. A key design principle is better focus on the content of applications, relying more on typography and less on graphics ("content before chrome"). Early examples of Metro principles can be found in Encarta 95 and MSN 2.0. The design language evolved in Windows Media Center and Zune and was formally introduced as "Metro" during the unveiling of Windows Phone 7. It has since been incorporated into several of the company's other products, including the Xbox 360 system software, Xbox One, Windows 8, Windows Phone, and Outlook.com under the names Microsoft design language and Modern UI after Microsoft discontinued the name "Metro" allegedly because of trademark issues. Microsoft later came to refer to Metro-styled applications as "universal apps", and in March 2015 expressed a preference for calling them simply "Windows apps."
The design language is based on the design principles of classic Swiss graphic design. Early glimpses of this style could be seen in Windows Media Center for Windows XP Media Center Edition, which favored text as the primary form of navigation. This interface carried over into later iterations of Media Center. In 2006, Zune refreshed its interface using these principles. Microsoft designers decided to redesign the interface and with more focus on clean typography and less on UI chrome. These principles and the new Zune UI were carried over to Windows Phone (from which much was drawn for Windows 8). The Zune Desktop Client was also redesigned with an emphasis on typography and clean design that was different from the Zune's previous Portable Media Center based UI. Flat colored "live tiles" were introduced into the design language during the early Windows Phone's studies.
Microsoft's design team cites as an inspiration for the design language signs commonly found at public transport systems. The design language places emphasis on good typography and has large text that catches the eye. Microsoft sees the design language as "sleek, quick, modern" and a "refresh" from the icon-based interfaces of Windows, Android, and iOS. All instances use fonts based on the Segoe font-family designed by Steve Matteson at Agfa Monotype and licensed to Microsoft. For the Zune, Microsoft created a custom version called Zegoe UI, and for Windows Phone Microsoft created the "Segoe WP" font-family. The fonts mostly differ only in minor details. More obvious differences between Segoe UI and Segoe WP are apparent in their respective numerical characters. The Segoe UI in Windows 8 had obvious differences – similar to Segoe WP. Characters with notable typographic changes included 1, 2, 4, 5, 7, 8, I, and Q.
Microsoft designed the design language specifically to consolidate groups of common tasks to speed up usage. It achieves this by excluding superfluous graphics and instead relying on the actual content to function as the main UI. The resulting interfaces favour larger hubs over smaller buttons and often feature laterally scrolling canvases. Page titles are usually large and consequently also take advantage of lateral scrolling. Animation plays a large part. Microsoft recommends consistent acknowledgement of transitions, and user interactions (such as presses or swipes) by some form of natural animation or motion. This aims to give the user the impression of an "alive" and responsive UI with "an added sense of depth."