This chapter analyzes how regulation and policy shape the adoption and evolution of ESG (environmental, social, and governance) practices in firms. It begins by arguing that regulatory and policy frameworks do not simply set legal boundaries—they actively define incentives and expectations that embed ESG within modern corporate governance. The chapter highlights that regulation’s influence is not limited to compliance. Policies act as catalysts, incentivizing firms to pursue ESG as a strategic opportunity. Importantly, the chapter shows that regulation also operates as a norm-setting force. Legal mandates help to institutionalize stakeholder expectations, making ESG a core measure of business legitimacy. Examples from environmental, workplace safety, and anti-discrimination law demonstrate how regulation changes both formal rules and organizational culture, often with long-term effects on firm behavior and performance. The chapter also presents original empirical evidence on how social legislation—such as the legalization of same-sex marriage in the United States—can produce measurable changes in firm outcomes by altering social norms and organizational climates. Using a difference-in-difference approach, the analysis shows that legal changes at the state level can lead to improved firm performance by fostering more inclusive and equitable workplaces. Together, these findings suggest that regulation and policy play a central role in ESG adoption: they establish minimum requirements, encourage innovation, and re-define legitimacy in business. Firms that anticipate and adapt to regulatory change can not only ensure compliance but also gain strategic and financial advantages in an evolving institutional landscape.