The company was founded in 1975, to develop and sell BASIC interpreters for the Altair 8800. Microsoft rose to dominate the home computer operating system market with MS-DOS in the mid-1980s, followed by the Windows line of operating systems. Many of its products have achieved near-ubiquity in the desktop computer market. One commentator notes that Microsoft's original mission was "a computer on every desk and in every home, running Microsoft software."[9] Microsoft possesses footholds in other markets, with assets such as the MSNBC cable television network, the MSN Internet portal, and the Microsoft Encarta multimedia encyclopedia. The company also markets both computer hardware products such as the Microsoft mouse as well as home entertainment products such as the Xbox, Xbox 360, Zune and MSN TV.[8] The company's initial public stock offering (IPO) was in 1986; the ensuing rise of the company's stock price has made four billionaires and an estimated 12,000 millionaires from Microsoft employees.[10][11][12]

Throughout its history the company has been the target of criticism, including monopolistic business practices and anti-competitive strategies including refusal to deal and tying. The U.S. Justice Department and the European Commission, among others, have ruled against Microsoft for various antitrust violations accordingly in today's political-cultural climate of mixed economies and "public interest of society".[13][14]

Following the launch of the Altair 8800, William Henry Gates III, (known as Bill Gates) called the creators of the new microcomputer, Micro Instrumentation and Telemetry Systems (MITS), offering to demonstrate an implementation of the BASIC programming language for the system. After the demonstration, MITS agreed to distribute Altair BASIC.[15] Gates left Harvard University, moved to Albuquerque, New Mexico where MITS was located, and founded Microsoft there. The company's first international office was founded on November 1, 1978, in Japan, titled "ASCII Microsoft" (now called "Microsoft Japan").[15] On January 1, 1979, the company moved from Albuquerque to a new home in Bellevue, Washington.[15] Steve Ballmer joined the company on June 11, 1980, and later succeeded Bill Gates as CEO.[15]

Among pre-IBM-PC products were the software package TASC (The AppleSoft Compiler), which compiled a BASIC program into Apple machine language, and the hardware Microsoft Softcard, an add-on Z80 processor card for the Apple II and compatible computers which allowed the use of the CP/M operating system instead of Applesoft and Apple DOS. In 1980, Microsoft entered the operating system business with its own version of Unix, called Xenix, which it licensed to various computer vendors.