Windows Vista is an operating system developed by Microsoft, released worldwide on January 30, 2007. Prior to its official announcement on July 22, 2005, it was known by its codename, Windows "Longhorn".

Development of the operating system spanned approximately five years, starting in early 2001. Over the course of this time period, the product was first codenamed Whistler+ (with some sources stating Idaho as a possible codename), and then Longhorn in May 2001. The first builds of the operating system known to use the Longhorn codename were compiled in May, 2002.

Initially envisioned as a minor upgrade to Windows XP, Microsoft later characterized "Longhorn" as a complete overhaul of the Windows operating system. One of the largest changes slated for "Longhorn" was pervasive use of managed code.

While in its earlier stages of development, "Longhorn" suffered from many problems relating to reliability and stability. This was due not only to the premature technology on which the operating system was based, but also because of the way new features were introduced and implemented. For this reason, the development of the operating system was "reset", with a preliminary build, 3790.1232.winmain.040819-1629 being compiled on August 19, 2004. Although this build is not known to contain any code from "Longhorn", it did include the "Longhorn" End User License Agreement (EULA), a testament to the build's authenticity.

Contrary to popular belief, only very early "Longhorn" builds were directly derived from Windows XP; later builds were based on Windows Server 2003 Release Candidate code. Builds compiled after the development reset are based on Windows Server 2003 Service Pack 1.

During Beta 1 development, Microsoft named the operating system Windows Vista. The new name was chosen to improve the product's image and reputation, and to reflect the new capabilities of the operating system.

A total of two Service Packs were released for the Windows Vista operating system. Service Pack 1 was made available to MSDN subscribers on Febuary 15, 2008, and was released to the Microsoft Download Center and Windows Update on March 18, 2008. Service Pack 2 was released to manufacturing on April 28, 2009, and released to the Microsoft Download Center and Windows Update on May 26, 2009. In addition, Microsoft released the Platform Update for Windows Vista on October 27, 2009, which was comprised of major new Windows 7 components and updated runtime libraries. The Platform Update requires Service Pack 2 prior to installation.