Microsoft Internet Explorer 5 (IE5) is the fifth, and by now, discontinued, version of the Internet Explorer graphical web browser, the successor to Internet Explorer 4 and one of the main participants of the first browser war. Its distribution methods and Windows integration were involved in the United States v. Microsoft Corp. case. Launched on March 18, 1999, it was the default browser in Windows 98 Second Edition, Windows 2000 and Windows ME and can replace previous versions of Internet Explorer on Windows 3.1x, Windows NT 3.51, Windows 95, Windows NT 4.0 and the original release of Windows 98. Although Internet Explorer 5 ran only on Windows, its siblings Internet Explorer for Mac 5 and Internet Explorer for UNIX 5 supported Mac OS X, Solaris and HP-UX.

Windows 2000 is a major release of the Windows NT operating system developed by Microsoft and designed for businesses as the direct successor to Windows NT 4.0. It was released to manufacturing on December 15, 1999, officially released to retail on February 17, 2000, and released on September 26, 2000, for Windows 2000 Datacenter Server. It was Microsoft's business operating system until the introduction of Windows XP Professional in 2001.