Windows NT 3.1 is the first major release of the Windows NT operating system developed by Microsoft, released on July 27, 1993.

At the time of Windows NT's release, Microsoft's Windows 3.1 desktop environment had established brand recognition and market share; but Windows 3.1 relied on the DOS operating system for essential functions, and it had a constrictive 16-bit architecture. Windows NT, however, was a complete, 32-bit operating system that retained a desktop environment familiar to Windows 3.1 users.

By extending the Windows brand and beginning Windows NT at version 3.1, Microsoft implied that consumers should expect a familiar user experience. The name Windows NT ("New Technology") advertised that this was a re-engineered version of Windows.

Windows NT began as a rewrite of the OS/2 operating system, which Microsoft had co-developed with IBM in the 1980s. For several reasons, including the market success of Windows 3.0 in 1990, Microsoft decided to advance Windows rather than OS/2. They relinquished their OS/2 development responsibilities to IBM, and forked their work on OS/2 v3.0 into a competing operating system. Windows NT 3.1 sold about 300,000 copies before it was succeeded by Windows NT 3.5 in 1994.

Windows NT 3.1 was available in two editions: Windows NT 3.1 for workstations, and Windows NT 3.1 Advanced Server for servers. When these premiered, their sales were limited by high system requirements, and a general lack of 32-bit applications to take advantage of the OS's data processing capabilities.

On December 31, 2000, Microsoft declared Windows NT 3.1 obsolete and stopped providing support and updates for the system.