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Since the 1970s, the financial system has undergone deep structural changes. Innovation has been a key driver of those changes and most economists acknowledge that the impact has been positive overall. However, each time, when a financial crisis arises, the debate is on. Especially, derivatives are among the major innovations, but they cause concern. A first issue is about the impact of derivatives on the volatility of the underlying assets. But, empirical findings do not support any significant effect. Nonetheless, the sophistication of the derivatives markets and the concentration of risk are potential sources of instability because of the rise of uncertainty, the repeated occurrences of extreme losses and the possibility of systematic risk. Classification JEL: A1, D8, G1.