Purpose – This study aims to examine the effect of Environmental, Social, and Governance (ESG) performance on firm value and to investigate the moderating role of the PROPER rating in the relationship between ESG performance and firm value among non-financial companies in Indonesia. Design/Methodology/Approach – This study employs secondary data from non-financial companies listed on the Indonesia Stock Exchange over the selected observation period, with the number of observations determined based on the sample selection criteria. Firm value is measured using Tobin’s Q, ESG performance is measured using ESG scores obtained from relevant data sources, and the PROPER rating is used as a moderating variable. Panel data regression analysis is conducted using a fixed effects model, which is selected based on the Chow test and Hausman test. Findings or Expected Outcomes – The results indicate that ESG performance has a significant effect on firm value. Furthermore, the PROPER rating is found to moderate the relationship between ESG performance and firm value, suggesting that stronger environmental performance enhances the impact of ESG on firm value. Originality/Value – This study contributes to the literature by integrating ESG performance and the PROPER rating into a single research model to explain firm value, particularly in the context of non-financial companies in Indonesia, which remains relatively underexplored. Practical/Social Implications – The findings provide practical insights for corporate management and regulators to emphasize the implementation of ESG practices and environmental performance as strategic tools to enhance firm value and strengthen stakeholder trust. Directions for Future Research/Limitations – This study is limited by the use of secondary data and the focus on non-financial companies in Indonesia. Future research is encouraged to extend the observation period, include different industry sectors, or employ alternative ESG measurements and moderating variables to enrich the research findings.