This Open Access book explores the evolving landscape of non-financial reporting and ESG (Environmental, Social, and Governance) performance, with a specific focus on small and medium-sized enterprises (SMEs) and micro-enterprises. Drawing on European regulatory frameworks, stakeholder theory, and empirical case studies, the book examines how SMEs navigate sustainability demands in a context traditionally dominated by large corporations and global standards. The book addresses the historical evolution of CSR, the challenges of ESG integration for investors, and the methodological development of a composite ESG indicator tailored to SMEs. It introduces innovative tools such as the Mazziotta–Pareto Index and participatory accounting frameworks like CARE and SEMA, offering practical insights into ESG measurement and reporting. Through comparative case studies and analysis, it bridges the gap between ESG theory and SME realities, contributing to both academic research and professional practice. Ideal for scholars in economics, finance, and sustainability, as well as practitioners and policymakers, this book advances the conversation on responsible innovation, regional development, and the future of ESG in the SME sector.