Although most of this large collection consists of papers of Lewis's legal practice, there are important groups which relate to the furnishing and maintenance of his city and country houses and the management of his farm, to the assembling of his outstanding collections of Asian and medieval illuminated manuscripts and of Babylonian clay tablets (now at the Free Library of Philadelphia), and to institutions with which he was closely associated, such as the American Philosophical Society, the University of Pennsylvania, and the Pennsylvania Academy of Fine Arts. Many letters and papers are about business (mortgages, rents, directorships in banks and insurance companies, and investments) and about the social and cultural life of Philadelphia (operas, libraries, museums, and schools for the handicapped).