Microsoft became the most valuable publicly traded company in the world in December 1999.
Microsoft’s market capitalization reached its historic peak during the technology-stock boom at the end of the 1990s. Its dominance in computer operating systems and office software gave it strong earnings, while investors placed exceptionally high values on technology companies expected to benefit from internet adoption.
The late-1990s market was highly volatile. Microsoft’s valuation later fell substantially after the dot-com bubble burst, and the company faced a major U.S. antitrust case concerning its conduct in the personal-computer software market.
This milestone refers to market capitalization, not the largest annual revenue or the greatest number of employees. Microsoft later returned to the top tier as cloud computing, enterprise software, and services became increasingly important to its business.