Windows NT 3.1 is the first release of Microsoft's Windows NT line of server and business desktop operating systems, and was released to manufacturing on July 27, 1993. The version number was chosen to match the one of Windows 3.1, the then-latest GUI from Microsoft, on account of the similar visual appearance of the user interface. Two editions of NT 3.1 were made available, Windows NT 3.1 and Windows NT Advanced Server.

Development of Windows NT started in November 1988, after Microsoft hired a group of developers from Digital Equipment Corporation led by Dave Cutler. Many elements of the design reflect earlier DEC experience with VMS and RSX-11. The operating system was designed to run on multiple instruction set architectures and multiple hardware platforms within each architecture. The platform dependencies are largely hidden from the rest of the system by a kernel mode module called the HAL.
Windows NT was originally intended to be OS/2 3.0, the third version of the operating system developed jointly by Microsoft and IBM. When Windows 3.0 was released in May 1990, it was so successful that Microsoft decided to change the primary application programming interface for the still-unreleased NT OS/2 (as it was then known) from an extended OS/2 API to an extended Windows API. This decision caused tension between Microsoft and IBM, and the collaboration ultimately fell apart. IBM continued OS/2 development alone, while Microsoft continued work on the newly-renamed Windows NT.