Windows NT 3.5 is the second release of the Microsoft Windows NT operating system. It was released on 21 September 1994 in two versions: Workstation and Server.

One of the primary goals during Windows NT 3.5's development was to increase the speed of the operating system; as a result, the project was given the codename "Daytona" in reference to the Daytona International Speedway in Daytona Beach, Florida.

This is the first Windows NT to adopt the names Windows NT Workstation and Windows NT Server for its editions. The editions of the previous Windows NT release, Windows NT 3.1, were named Windows NT and Windows NT Advanced Server.

The interface was updated to be consistent with

the Windows for Workgroups 3.xx. It also upgraded Object Linking and Embedding (OLE) support from version 1.0 to version 2.0 and is more efficient - performance is higher and it requires less memory than Windows NT 3.1.

Windows NT 3.5 refuses to install on a processor newer than the original Pentium (P5 core). Windows NT 3.51 fixed that. It is however possible to modify files on the install CD which will allow it to install.