# Girsanov's Theorem

*Quant & Pricing — Finicade finance glossary*

The mathematical licence to switch from the real world to the risk-neutral one by changing the drift of a random process. It's the deep machinery that makes risk-neutral pricing rigorous.

**Also known as:** change of measure, radon-nikodym

**Related terms:** [Risk-Neutral Pricing](https://finicade.com/glossary/risk-neutral-pricing), [Martingale](https://finicade.com/glossary/martingale), [Brownian Motion](https://finicade.com/glossary/brownian-motion)

**Taught in:** Quant Quest — Stochastic Calculus II

Source: https://finicade.com/glossary/girsanov-theorem