Abstract
<jats:p>This study consolidates three related questions about environmental, social and governance (ESG) disclosure and firm value in Vietnam: whether ESG is associated with market value in a linear baseline, whether financial performance transmits that association, and whether the economic interpretation changes under nonlinear specifications and alternative valuation measures. The analysis uses an unbalanced panel of 192 Vietnamese listed firms from 2018 to 2024, comprising 1,260 firm-year observations. Firm fixed effects models with firm-clustered standard errors identify a positive baseline association between ESG disclosure and the principal valuation measure. Profitability, measured by return on equity, is the only supported financial channel; operating efficiency and growth do not satisfy the first-stage condition for mediation. The baseline direct association is concentrated in 2022-2024. Quadratic sensitivity tests add an important qualification. Positive curvature appears across three additional valuation proxies, but the economic shape depends on measurement. The transformed valuation index is monotonically convex, whereas two ratio-based Tobin's Q measures produce interior U shapes with minima near ESG scores of 0.33 to 0.35. The two ratio measures are highly correlated with each other but only weakly correlated with the transformed index. The consolidated evidence therefore supports a bounded conclusion: ESG is associated with higher firm value chiefly when it coincides with stronger profitability and when firms operate beyond low-engagement ESG levels, but the strength and shape of the relationship depend materially on the valuation proxy. The study shows why mediation, functional form and measurement sensitivity should be evaluated together rather than reported as separate ESG valuation claims.</jats:p>