While jointly developing a new OS with IBM in 1984, OS/2, Microsoft released Microsoft Windows, a graphical extension for MS-DOS, on November 20.^[11] Microsoft moved its headquarters to Redmond on February 26, 1986, and on March 13 the company went public;^[12] the ensuing rise in the stock would make an estimated four billionaires and 12,000 millionaires from Microsoft employees.^[13] Due to the partnership with IBM, in 1990 the Federal Trade Commission set its eye on Microsoft for possible collusion; it marked the beginning of over a decade of legal clashes with the U.S. Government.^[14] Microsoft announced the release of its version of OS/2 to original equipment manufacturers (OEMs) on April 2, 1987;^[15] meanwhile, the company was at work on a 32-bit OS, Microsoft Windows NT, using ideas from OS/2; it shipped on July 21, 1993 with a new modular kernel and the Win32 application programming interface (API), making porting from 16-bit (MS-DOS-based) Windows easier. Once Microsoft informed IBM of NT, the OS/2 partnership deteriorated.^[16]

Microsoft introduced its office suite, Microsoft Office, in 1990. The software bundled separate office productivity applications, such as Microsoft Word and Microsoft Excel.^[17] On May 22 Microsoft launchedWindows 3.0 with a streamlined user interface graphics and improved protected mode capability for the Intel 386 processor.^[18] Both Office and Windows became dominant in their respective areas.^[19][20] Novell, a Word competitor from 1984–1986, filed a lawsuit years later claiming that Microsoft left part of its APIs undocumented in order to gain a competitive advantage.