Microsoft became the world's most valuable publicly traded company in 1999 after surpassing General Electric.
The milestone reflected the enormous growth of Windows and Office during the personal-computer boom. Microsoft had already become a dominant software supplier, and its market value rose sharply as businesses and households adopted PCs.
Microsoft was founded in 1975 by Bill Gates and Paul Allen. Its early breakthrough came from licensing an operating system to IBM for its personal computer, helping establish MS-DOS as a major industry standard.
The company later expanded into cloud computing, gaming, hardware, search, and professional networking. Microsoft Azure and Office 365 became especially important growth businesses. Market-cap leadership changes over time because share prices move daily, so this historical distinction should not be confused with a permanent ranking.