This paper focuses on the financial markets crash of October 1987 to examine the effects of trading strategies and other institutional structures on price behavior during this period. It presents a system dynamics model which looks at average, aggregate stock prices. It specifies connections among various trading sites and techniques. In particular, it examines the influence of financial and technological innovations such as stock-index futures and other derivative instruments and high speed order execution and transaction systems on market performance. A major conclusion is that the financial markets are characterized by complex structures only partially economic in nature. This suggests that the interplay between market pricing behavior and institutional behavioral reactions are more complex than is currently believed.