The presence and significance of implied volatility skew is one of the most important and interesting aspects of listed options. We have covered this topic on many occasions in previous issues, so this article will not retread well-worn ground. Implied volatility skew refers here to the differences in the implied volatilities of options in the same expiration cycle with different strike prices. While there are many competing attempts in the literature to model the behavior of changes in skew, these models should not be confused with explanations: the reason why skew exists, in options on any asset, is that market participants are only willing to trade contracts at some multiple of implied volatility above or below at-the-money levels. That participant order flow is the singular cause of volatility skew is practically a tautology.