Abstract
We develop a portfolio-choice theory of Environmental, Social, and Governance (ESG) investing that integrates ESG-related return beliefs, risk considerations, and intrinsic ESG preferences. ESG investment is modeled as a continuous portfolio tilt away from a baseline allocation, affecting expected returns, portfolio risk, and investor utility within a mean-variance framework. ESG tilts interact with baseline risk exposures and generate convex diversification costs. The model delivers a closed-form solution for optimal ESG exposure that depends on ESG return beliefs, intrinsic preferences, investor risk aversion, and the return covariance structure. ESG investment can be optimal even without positive ESG return premia when ESG tilts hedge portfolio risk or provide direct utility. The framework explains heterogeneous ESG adoption and reconciles mixed empirical evidence on ESG returns.