On August 24, 2001, Microsoft released Windows XP to manufacturing. The system, codenamed Whistler, replaced both Windows 2000 for professionals and Windows ME for home users and finally moved consumers onto the Windows NT codebase, ending the Windows 9x line that ran from Windows 95 through 98 and Me.

XP introduced the two-column Start Menu, a reworked taskbar with application grouping, new icons and visual effects. Microsoft also invested in backward compatibility for legacy applications. At launch there were two editions, Home and Professional. Upgrades from Windows 98 and ME allowed either edition, while Windows NT 4 and 2000 users were limited to Professional, which added domain account support and multi-processor capability.

The operating system proved remarkably persistent. Extended support ended on April 8, 2014, more than twelve years after release. The embedded variant Windows Embedded POSReady 2009 received support until April 9, 2019. In May 2019 Microsoft even shipped an out-of-band patch for XP to close a Remote Desktop Services flaw, and security updates for XP SP3 were still appearing as late as 2024.

Adoption lingered in critical infrastructure. At the end of 2016, 90 percent of the UK's National Health Service still ran XP. In 2018 the Reserve Bank of India ordered banks to remove XP from ATMs by 2019. A former Microsoft employee told The Register that part of the global banking sector continued to run Windows Server 2003, XP's server sibling.

Retail availability followed in October 2001. For many users, XP with its Bliss wallpaper remains the high point of the Windows line. Its successor, Windows Vista, arrived with a considerably cooler reception.