Intellectual history in the United States has long borne a peculiarly close kinship to social history. The twin fields rose together a century ago in a filial revolt against the cloistered, conservative study of political institutions. Sharing a progressive interest in social thought and social reform, they joined in the self-styled “social and intellectual history” of the interwar decades. After mid-century, however, they moved in divergent directions. Many social historians adopted the quantitative methods of the social sciences, documenting the diverse experiences of workers, women, immigrants, slaves, native peoples, and others often marginalized in the textual record as well as the property regimes, modes of production, patterns of inheritance and mobility, and large-scale demographic and environmental forces that governed their lives. Intellectual historians tended to favor the qualitative evidence gleaned from the more cohesive letters and libraries of traditional elites, specializing in close readings of the intricate discursive, aesthetic, and spiritual templates of social experience found in religion, science, philosophy, political theory, and art and literature. Both subdisciplines had come into parallel crises by the 1980s, chastened by postmodern attacks on “master narratives” of any kind, whether idealist or materialist. In the decades since, social historians have sought a more nuanced consideration of thought and culture, while intellectual historians have at once broadened the range of their subjects and sources and limited more carefully the claims they make for them.