The US30 is a U.S. stock index composed of 30 of the largest publicly traded U.S. companies. It was created in 1896 and was meant to be an easy way to track the U.S. stock market performance at a time when information flow was not as rapid or pervasive. The components of the US30 can and do change as companies grow and shrink. The Dow 30 is still considered to be an accurate gauge of the health of the U.S. equity markets.