Microsoft became the world's most valuable public company during the dot-com boom in December 1999.
At the height of the late-1990s technology boom, investors placed extraordinary values on software and internet-related businesses. Microsoft benefited from the dominance of Windows on personal computers, the popularity of Office software, and expectations that its products would remain central to the expanding digital economy.
In December 1999, Microsoft's market capitalization reached approximately $600 billion, making it the world's most valuable public company at the time. The figure was enormous by historical standards, although later market-cap records would make it look smaller because of inflation, economic growth, and the expansion of global equity markets.
The period also illustrates why market capitalization is not the same as revenue or profit. A stock price reflects what investors collectively expect a company may earn in the future. When the dot-com bubble burst in 2000, many technology shares fell dramatically. Microsoft remained a major corporation, but its market value moved substantially below the 1999 peak.