Nasdaq

The Nasdaq Composite launched in 1971 alongside the Nasdaq exchange itself, and tracks nearly every common stock listed on Nasdaq — several thousand companies, ranging from the largest technology firms in the world down to small-cap and micro-cap names, plus a number of non-U.S. companies that list directly on the exchange.

Because most major U.S. technology listings trade on Nasdaq rather than the NYSE, the Composite is noticeably more concentrated in technology, biotechnology, and internet-related companies than broader benchmarks like the S&P 500. It's market-capitalization-weighted, so the largest constituents — again, disproportionately technology companies — drive most of its day-to-day movement.

The Composite is often confused with the narrower, more commonly quoted Nasdaq-100, which includes only the 100 largest non-financial companies listed on the exchange. The Composite is broader: it includes financial companies and the full long tail of smaller Nasdaq-listed names that the Nasdaq-100 deliberately excludes.

Because of its tech concentration, the Nasdaq Composite tends to be more volatile than the S&P 500 or Dow, and is watched as a bellwether for growth-stock and technology-sector sentiment specifically, rather than the broader economy.