Microsoft briefly became the world’s most valuable listed company in October 1999.
The company’s market capitalization rose during the late-1990s technology boom, when investors placed exceptionally high valuations on fast-growing software and internet businesses. Microsoft benefited from the dominance of Windows on personal computers and the broad adoption of its Office productivity software.
Its valuation reached roughly $600 billion during that period, a figure that was extraordinary at the time. Market-cap comparisons from earlier decades must be read in historical context because inflation, share counts, stock splits, and changing market structures affect direct comparisons.
Microsoft was later overtaken by other companies as technology leadership shifted toward consumer electronics, internet platforms, semiconductors, and cloud computing. It remains a major listed company, with businesses spanning Windows, Azure, Office, gaming, and professional networking.