Microsoft became the world’s most valuable public company by market capitalization in 1999.
Microsoft reached that position during the late-1990s technology boom, when investors placed enormous value on its dominance in personal-computer operating systems and productivity software. Windows and Microsoft Office were installed across businesses and households worldwide.
The company was founded in 1975 by Bill Gates and Paul Allen. Its 1986 initial public offering helped create one of the defining corporate fortunes of the personal-computer era. Microsoft’s market value later fell during the dot-com crash, even though the company remained commercially powerful.
This fact is historical rather than a permanent ranking. Market-capitalization leadership changes with share prices, exchange rates, and investor expectations. Microsoft later returned to the top tier after expanding into enterprise software, cloud computing through Azure, gaming, and subscription products such as Microsoft 365.