This volume examines sustainability reporting among SMEs in the European Union, focusing on the interplay between mandatory and voluntary ESG disclosure. Targeted to scholars, practitioners, and policymakers, it brings together interdisciplinary contributions that integrate theoretical frameworks, regulatory analyses, and empirical evidence to provide a comprehensive understanding of ESG practices within European SMEs. The chapters explore the pivotal role of SMEs in the EU economy, recent policy and regulatory developments, including the CSRD, ESRS standards, and the Omnibus package, and the relevance of SME Growth Markets in facilitating smaller firms' access to capital markets. Drawing on both conceptual and empirical insights, the volume advances knowledge on the effectiveness of ESG disclosure and contributes to the broader academic and policy debate on the challenges SMEs face in adapting to evolving sustainability frameworks and regulatory requirements.