Windows NT is a proprietary graphical operating system produced by Microsoft as part of its Windows product line, the first version of which, Windows NT 3.1, was released on July 27, 1993. Originally made for the workstation, office, and server markets, the Windows NT line was made available to consumers with the release of Windows XP in 2001. The underlying technology of Windows NT continues to exist to this day with incremental changes and improvements, with the latest version of Windows based on Windows NT being Windows 11 in 2021.

The name "Windows NT" originally denoted the major technological advancements that it had introduced to the Windows product line, including eliminating the 16-bit memory access limitations of earlier Windows releases such as Windows 3.1 and the Windows 9x series. Each Windows release built on this technology is considered to be based on, if not a revision of Windows NT, even though the Windows NT name itself has not been used in many other Windows releases since Windows NT 4.0 in 1996.

Windows NT provides many more features than other Windows releases, among them being support for multiprocessing, multi-user systems, a "pure" 32-bit kernel with 32-bit memory addressing, support for instruction sets other than x86, and many other system services such as Active Directory and more. Newer versions of Windows NT support 64-bit computing, with a 64-bit kernel and 64-bit memory addressing.