The story of Microsoft’s mobile operating systems is a decades-long saga that saw the company transition from a dominant pioneer in business handhelds to a bold innovator that ultimately failed to break the iOS and Android duopoly.

The 2007 launch of the iPhone rendered the stylus-based Windows Mobile obsolete almost overnight. In response, Microsoft completely scrapped its old code to launch in 2010.

: In 2011, Microsoft partnered with Nokia, leading to iconic hardware like the Lumia series. Microsoft later acquired Nokia's handset division for over $7 billion in 2013.

Before modern smartphones, Microsoft established a foundation with in 1996, designed for tiny "handheld PCs". This evolved into Pocket PC 2000 and eventually Windows Mobile in 2003, which successfully mirrored the desktop Windows experience with a Start menu, File Explorer, and stylus-driven navigation. By 2007, Microsoft held a 60 percent market share in the U.S. smartphone market, catering primarily to business professionals who needed portable versions of Office and Outlook. The Reinvention: Windows Phone 7 & 8 (2010–2014)

In 2015, Microsoft attempted its most ambitious unification yet with .

: It introduced the "Metro" UI, featuring vibrant Live Tiles that updated in real-time. Reviewers from The Verge called it the most original reimagining of a smartphone after the iPhone.