Microsoft Windows is a succession of software operating systems (OS) and graphical user interfaces. The primary version made available in November 1985 as an MS-DOS was an add-on to respond to the increase in graphical user interfaces (GUIs). Windows uses a GUI, making way for easier and more convenient computer usage. Users navigate through the OS using the Start menu and desktop icons.

Microsoft Windows has come to dominate the global personal computer scene. Its prevalence overtook the earlier Mac OS. The newest client version is Windows Vista, while the newest version of the server is Windows Server 2008.

Microsoft targeted two markets with its Operating Systems. One focus is the home consumer and the other is the professional IT client. Home versions usually have wider support for multimedia and less utility for security and networking, while professional versions have less support for multimedia and more utility in terms of security and networking.

The earliest version of this OS was Microsoft Windows 1.0 released to compete with the then-current Apple OS, although very basic in functionality. It achieved modest popularity back then.

Windows 2.03, released in January 1988, changed the interface to overlying windows from tiled. This evolution led to a lawsuit against Microsoft from Apple Computers, alleging copyright infringement.

Windows 3.0, released in 1990, was the first Windows OS that achieved commercial success. It sold 2 million copies the first half-year of its release.

Microsoft released Windows Vista in January 2007. It contains new features, such as a revamped shell and redesigned user interface, as well as major technical changes with an emphasis on security.