Microsoft became the first company to reach a $500 billion market capitalization in the United States.
Microsoft crossed the $500 billion level in 1999 during the late-1990s technology boom. Investors were valuing the company's dominant Windows operating system and its rapidly expanding Office software business.
The milestone came before the dot-com crash, when technology shares were receiving exceptionally high valuations. Microsoft later broadened its business through enterprise software, cloud computing, gaming and hardware.
Market capitalization is not the same as company revenue or profit. It represents the value investors assign to all outstanding shares. Microsoft eventually became one of the first companies to pass much larger valuation milestones, including $1 trillion in 2019.