Empirical studies indicate that the asset volatility is a random process and, in general, cannot be described by a single number. Yet, option pricing models assuminga deterministic asset volatility originated by Black-Scholes (1973) and Merton (1973)(BSMM) are very popular in practice because of their relative simplicity. In principle, vanilla option traders understand the limitations of BSMM and know how to adjust the model and manage their risks appropriately. However, more complex financial products, such as forward-starting options, or options on the realized variance of an asset, derive their value from the asset volatility rather than its price, so that for pricing and risk-managing of such products traders tend to use stochastic volatility models.