This chapter establishes the conceptual and historical foundations of ESG by tracing the evolution of Corporate Social Responsibility (CSR) as an antecedent to modern sustainability reporting. Structured in two main sections, it first explores the origin of CSR, from the early philanthropic initiatives before 1950 to the post-COVID-19 era of integrated responsibility. Anchored in seminal academic contributions including Bowen (1953), Frederick (1960), Carroll (1977; 1991; 2008), and Smith (2009), the chapter examines how definitions of CSR have expanded over time to encompass economic, managerial, and socio-cultural dimensions. The theoretical underpinnings of CSR are presented through the lens of stakeholder theory and the shifting expectations of corporate accountability in society. The second section addresses the regulatory and institutional trajectory that has shaped ESG practices today. It outlines the progressive stages in the formalization of CSR directives, starting with the emergence of voluntary guidelines in the 1970s–1990s, followed by the expansion of formal frameworks and global initiatives in the 2000s. The 2010s marked a shift toward mandatory disclosure mechanisms and regionally enforced accountability, culminating in the current era of harmonization and ESG integration. This final phase reflects a broader consensus around global sustainability imperatives, supported by policy innovations and increased stakeholder pressure.