Windows Vista ( ) is a line of operating systems developed by Microsoft for use on personal computers, including home and business desktops, laptops, Tablet PCs, and media centers. Prior to its announcement on July 22, 2005, Windows Vista was known by its codename "Longhorn". Development was completed on November 8, 2006; over the following three months it was released in stages to computer hardware and software manufacturers, business customers, and retail channels. On January 30, 2007, it was released worldwide to the general public, and was made available for purchase and downloading from Microsoft's web site. The release of Windows Vista comes more than five years after the introduction of its predecessor, Windows XP, the longest time span between successive releases of Microsoft Windows.

Windows Vista contains many changes and new features, including an updated graphical user interface and visual style dubbed Windows Aero, improved searching features, new multimedia creation tools such as Windows DVD Maker, and redesigned networking, audio, print, and display sub-systems. Vista also aims to increase the level of communication between machines on a home network, using peer-to-peer technology to simplify sharing files and digital media between computers and devices. Windows Vista includes version 3.0 of the .NET Framework, which aims to make it significantly easier for developers to write applications than with the traditional Windows API.

Microsoft's primary stated objective with Windows Vista, however, has been to improve the state of security in the Windows operating system. One common criticism of Windows XP and its predecessors has been their commonly exploited security vulnerabilities and overall susceptibility to malware, viruses and buffer overflows. In light of this, Microsoft chairman Bill Gates announced in early 2002 a company-wide "Trustworthy Computing initiative" which aims to incorporate security work into every aspect of software development at the company. Microsoft stated that it prioritized improving the security of Windows XP and Windows Server 2003 above finishing Windows Vista, thus delaying its completion.

Criticism of Windows Vista has targeted its protracted development time, more restrictive licensing terms, the inclusion of a number of new digital rights management technologies aimed at restricting the copying of protected digital media, lack of device drivers for some hardware, and the usability of other new features such as User Account Control.