Windows 7 (codenamed Vienna, formerly Blackcomb) is a personal computer operating system developed by Microsoft. It is a part of Windows NT family of operating systems. Windows 7 was released to manufacturing on 22 July 2009, and became generally available on 22 October 2009,less than three years after the release of its predecessor, Windows Vista. Windows 7's server counterpart, Windows Server 2008 R2, was released at the same time.

Windows 7 was primarily intended to be an incremental upgrade to the operating system, intending to address Windows Vista's critical reception (such as performance improvements), while maintaining hardware and software compatibility. Windows 7 continued improvements on Windows Aero (the user interface introduced in Windows Vista) with the addition of a redesigned taskbar that allows applications to be "pinned" to it, and new window management features. Other new features were added to the operating system, including libraries, the new file sharing system HomeGroup, and support for multitouch input. A new "Action Center" interface was also added to provide an overview of system security and maintenance information, and tweaks were made to the User Account Control system to make it less intrusive. Windows 7 also shipped with updated versions of several stock applications, including Internet Explorer 8, Windows Media Player, and Windows Media Center.

In contrast to Windows Vista, Windows 7 was generally praised by critics, who considered the operating system to be a major improvement over its predecessor due to its increased performance, its more intuitive interface (with particular praise devoted to the new taskbar), fewer User Account Control popups, and other improvements made across the platform. Windows 7 was a major success for Microsoft; even prior to its official release, pre-order sales for 7 on the online retailer Amazon.com had surpassed the previous records. In just six months, over 100 million copies had been sold worldwide, increasing to over 630 million licenses by July 2012, and a market share of 56.53% of "desktop operating systems" as of September 2015 according to Net Applications, making it the most widely used version of Windows.