21. Hedging strategies# 21.1. Introduction# 21.2. Mininum Variance Hedging# 21.3. Factor models# 21.3.1. Principal Component Analysis# 21.4. Hedging with transaction costs# 21.5. Pre-hedging# 21.6. Skew vs hedge in the Avellaneda-Stoikov framework# 21.7. Non linear hedges# 21.8. Exercises#