This paper provides a narrative of the emergence of the standard textbook definition of public goods. It focuses on Richard A. Musgrave's contribution in defining public goods as nontrivial and nonexcludable-from 1937 to 1973. Although Samuelson's mathematical definition is generally used in models of public goods, the qualitative understanding of the specificity of pure public goods owes a lot to Musgrave. I argue that the evolution of Musgrave's writings on public goods reflects his intention to justify his view of the role of the state in providing goods and services to citizens with an argument that would be convincing to the community of U.S. economists in the mid-twentieth century. Musgrave's definition highlights his lifelong concern for a comprehensive, realistic, and useful normative theory of the public sector.