Risk about future payoffs is at the center of asset pricing, asset allocation, and option pricing. Prices at the stock and bond market, and in particular option prices, can react significantly to a change in uncertainty. Over the last years, the VIX volatility index, which is the square-root of a model-free variance calculated from the cross-section of SPX option prices, became a well-known measure for uncertainty. In the financial crises, the VIX, which has usually been around 20%, has exceeded the level of 80% several times. During this time, but also during former periods of market stress like the stock market crash of 1987, or the collapse of LTCM, volatility derivatives, which allow to trade variance risk, thus naturally attracted attention.