Which U.S. exchange introduced the first modern stock-market circuit breakers after the 1987 crash?

The New York Stock Exchange introduced the first modern stock-market circuit breakers after the 1987 crash.

The exchange adopted trading-halt rules in the aftermath of Black Monday, when the Dow Jones Industrial Average plunged 22.6% in one session. These rules were intended to pause trading during extreme declines and give investors time to absorb information before trading resumed.

The original system used fixed point thresholds for the Dow, so its limits became less suitable as the index changed over time. U.S. markets later moved toward percentage-based thresholds, and modern rules coordinate halts across major exchanges. A market-wide halt can occur when the S&P 500 falls by specified percentages during a trading day.

Circuit breakers do not prevent ordinary losses and cannot eliminate the causes of a crash. Their purpose is to interrupt exceptionally rapid selling, reduce confusion, and provide a brief opportunity for orderly price discovery. Individual stocks can also have separate trading-pause mechanisms.