Numerous commentators have claimed that the recent application of computer techniques to monitor price differences and trigger trades between the spot, futures and options markets for stocks (called programmed trading) has increased the volatility of stock prices. G. J. Santoni examines this issue in the second article in this Review, “Has Programmed Trading Made Stock Prices More Volatile?” Santoni discusses the theory that underlies programmed trading and examines various measures of stock price variation. These results suggest that programmed trading has not increased price volatility in the spot market for stocks.