A Contract For Difference (CFD) allows an investor to speculate on the price movement of the S&P 500 index without owning the underlying asset. If the index rises in value, the investor profits, and if it falls, the investor loses money. The investor can open both long and short positions on the S&P 500, with profits and losses determined by the difference between the opening and closing price of the index. CFDs provide high leverage, so even small movements in the underlying asset result in large percentage gains or losses in the value of the CFD.