The term “pro bono publico” has a long-standing tradition within the American legal profession, although its definition and organizing principles have dramatically changed over time. In this chapter, we review the historical development of the contemporary US pro bono regime and then discuss the recent emergence among elite American law firms of corporate social responsibility (CSR) as a rationale for pro bono practice. In contrast to the legal professionalism rationale for pro bono, wherein lawyers owe a distinct professional obligation to provide meaningful access to the legal system, the CSR rationale locates pro bono under the umbrella of broader commitments to public service, including diversity, philanthropy, environmental sustainability, and global corporate citizenship.