Microsoft held the title of the world's most valuable company at the end of 1999.
At the height of the dot-com boom, Microsoft’s market capitalization reached roughly $600 billion, making it the largest publicly traded company by market value at the end of the 1990s. Its dominant Windows operating system and Office productivity software generated substantial profits and recurring demand.
Microsoft’s rise followed its 1986 stock-market listing and the rapid spread of personal computers. The company also benefited from licensing agreements that placed Windows on computers made by many manufacturers.
The late-1990s ranking is easy to confuse with later milestones involving General Electric, Apple, and other firms. Market-cap rankings change with share prices, exchange rates, share counts, and corporate actions, so a company can be the leader at one date without holding the position permanently.