The anthropology of caste was a pivotal part of colonial knowledge in British India in the late nineteenth and early twentieth centuries. Denzil Ibbetson and Herbert Risley, then the two leading official anthropologists, both made major contributions to the study of caste, which this article discusses. Ibbetson and Risley assumed high office in the imperial government in 1902 and played important roles in policy making during the partition of Bengal (1903–5) and the Morley-Minto legislative councils reforms (1906–9); Ibbetson was also influential in deciding Punjab land policy in the 1890s. Contemporary policy documents, which this article examines, show that the two men's anthropological knowledge had limited influence on their deliberations. Moreover, caste was irrelevant to their thinking about agrarian policy, the promotion of Muslim interests, and the urban, educated middle class, whose growing nationalism was challenging British rule. No ethnographic information was collected about this class, because the scope of anthropology was restricted to ‘traditional’ rural society. At the turn of the twentieth century, colonial anthropological knowledge, especially about caste, had little value for the imperial government confronting Indian nationalism, and was less critical in constituting the Indian colonial state than it previously had been.