We study how to estimate and interpret demand elasticities in dynamic settings where prices and flows are jointly determined. Because price changes necessarily alter expected returns or cash flows, there is no single context-free elasticity: measured elasticities depend on which expectations adjust. We formalize static, immediate, and dynamic elasticities and show that the dynamic elasticity equals the inverse of the equilibrium price multiplier. A tractable linear model delivers testable comparative statics linking price multipliers to risk, persistence, systematic exposure, and surprise. Empirically, we confirm these patterns and show that structural demand can be recovered from reduced-form price responses even under persistent shocks.