Windows 2000 is a line of operating systems produced by Microsoft for use on business desktops, notebook computers, and servers. Released on 17 February 2000, it was the successor to Windows NT 4.0, and is the final release of Microsoft Windows to display the "Windows NT" designation.

Microsoft marketed Windows 2000 as the most secure Windows version ever, but it became the target of a number of high-profile virus attacks such as Code Red and Nimda. Over ten years after its release, it continues to receive patches for security vulnerabilities nearly every month and will continue to do so until 13 July 2010.

Windows 2000 was succeeded by Windows XP for desktop systems in October 2001 and Windows Server 2003 for servers in April 2003