The focus of this study is on the effect of mandatory ESG (Environmental, Social and Governance) disclosures on the reporting behavior of companies in Scandinavia. It analyzes the evolution of ESG reporting from a voluntary framework between 2007-2016 to a mandatory one from 2017-2023 in Sweden, Norway, Denmark, and Finland to check whether enforcement improved the level and consistency of reporting. The study uses a panel dataset of 138 publicly listed companies from the four countries, applying descriptive analysis alongside several linear regression frameworks. Two distinct models are estimated – one based on ESG reporting within the voluntary framework and one based on the impact of mandatory disclosure. Control variables firm’s size, profitability, leverage, sales growth, as well as year-fixed effects are included. The findings reveal significant gaps in ESG disclosure during the voluntary reporting period among firms. Following the enforcement of mandatory ESG reporting frameworks, there was a significant enhancement in disclosure levels and uniformity across firms. Firm size was a significant factor explaining disclosure behavior while profitability, leverage, and growth were not. These results demonstrate that enforcement clearly drives better ESG reporting. This paper adds to the body of literature on ESG disclosures with fresh empirical data from a Nordic setting that has experienced both voluntary and mandatory regimes. It weaves together signaling, stakeholder, and institutional theories to explain corporate behavioral adaptations to regulatory shifts. The study uses ESG scores as disclosure proxies, which inadequately capture changes in reporting rigor. It also examines only publicly listed companies, which diminishes applicability to private businesses or other regions. Further research should analyze content measures of disclosure and expand geographic scope. The research underscores the need for enforcing regulated frameworks for mandatory ESG disclosures. As refined standards for disclosures are developed, policymakers will be able to use the insights for framing thresholds, while companies, especially smaller ones, will appreciate the need for capacity-building towards ESG compliance. Improved ESG disclosure enhances transparency, fostering enhanced corporate accountability and informed stakeholder actions. Mandatory disclosure advances wider sustainability goals, integrating corporate activities into essential environmental and social frameworks.