Program Trading
The automated simultaneous purchase or sale of a basket of stocks using computer-driven order systems.
What is Program Trading?
Program trading refers to the coordinated, computer-driven simultaneous buying or selling of a large basket of stocks, typically 15 or more securities worth at least $1 million in aggregate, a threshold historically used by the NYSE to classify such activity. Originally developed for index arbitrage—exploiting price differences between stock index futures and the underlying shares—program trading now encompasses portfolio rebalancing, risk hedging, and tactical asset allocation. Critics linked excessive program trading to the 1987 Black Monday crash, prompting exchanges to introduce circuit breakers that temporarily halt program trading when markets move too sharply. Today, most large institutional trades involve some form of program or algorithmic execution, making program trading a foundational component of modern equity market structure.
Example
When the S&P 500 index is rebalanced each quarter, index fund managers use program trading to simultaneously buy shares of newly added companies and sell shares of removed ones, coordinating dozens of trades to minimize market impact and tracking error relative to the benchmark.
Source: Investopedia — Program Trading