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 center PCs. 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, and was made available for purchase and download from Microsoft's website. The release of Windows Vista came more than five years after the introduction of its predecessor, Windows XP, the longest time span between successive releases of Microsoft Windows desktop operating systems.

Windows Vista contains many changes and new features, including an updated graphical user interface and visual style dubbed Windows Aero, a redesigned search functionality, multimedia tools including Windows DVD Maker, and redesigned networking, audio, print, and display sub-systems. Vista 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, allowing software developers to write applications without traditional Windows APIs.

Microsoft's primary stated objective with Windows Vista has been to improve the state of security in the Windows operating system. One common criticism of Windows XP and its predecessors is 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.

While these new features and security improvements have garnered positive reviews, Vista has also been the target of much criticism and negative press. Criticism of Windows Vista has targeted its high system requirements, its 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 compatibility with some pre-Vista hardware and software, and the number of authorization prompts for User Account Control. As a result of these and other issues, Windows Vista had seen initial adoption and satisfaction rates lower than Windows XP. However, with an estimated 350 million internet users as of January 2009, it has been announced that Vista usage had surpassed Microsoft’s pre-launch two-year-out expectations of achieving 200 million users. As of the end of May 2009, Windows Vista is the second most widely used operating system on the internet with a 24.35% market share, the most widely used being Windows XP with a 61.54% market share.