Frank Siebert (1913-1998) is one of the key contributors to the field of Algonquian linguistics. While he did not pursue a degree in linguistics or anthropology, he independently acquired the skills and knowledge of a professional scholar. His work on Penobscot is some of the best and most comprehensive in existence. The Siebert Papers document the interest and work of Frank Siebert in the linguistics of the Algonquian family of languages, particularly Penobscot. The collection includes correspondence, research notes, drafts and published manuscripts by Siebert, as well as secondary sources consulted by Siebert. To a lesser extent, it contains material that documents Siebert's personal life, his interest in book collecting and his career as a physician.

An archaeological anthropologist and linguist, John Alden Mason spent the majority of his career at the University Museum of the University of Pennsylvania. After receiving his undergraduate degree at Penn in 1907, Mason received a doctorate at Berkeley (1911) for his ethnographic work on the Salinan Indians of California, but his diverse interests in later years ran the gamut from Puerto Rican folklore to Piman languages and cultures (including Pima, Papago, Pima Bajo, Northern and Southern Tepehuan, and Tepecano), Mayan, Aztec, and Incan archaeology, and the languages of South American Indians. Mason was curator of the University Museum at Penn from 1926 until his retirement in 1958. The Mason Papers include both in-coming and outgoing correspondence, linguistic material, notes, and photographs relating to Mason's work in the southwestern U.S., northern Mexico, and South America. Centered on the years after Mason's return to Philadelphia in 1926, the collection covers all aspects of Mason's professional life, from reports on field work to answering casual questions referred to him through the University Museum to data and analyses on Piman and other languages. The collection also contains voluminous files relating to the Mason's editorship of the American Anthropologist (bulk: 1945-1948). Of special note are a series of class notes (1908-1910) kept by Mason for course work in ethnology, archaeology, and linguistics at the University of Pennsylvania under Edward Sapir and Frank Speck.

For many years referred to as the "Franz Boas Collection of American Indian Linguistics," this collection consists of a large body of linguistic and ethnographic material gathered together by Boas and many of his colleagues and students primarily from the 1890s to the 1940s. It contains the bulk of Boas's own fieldwork material, with the main exception of most of his Inuit and earliest Northwest Coast fieldwork. It contains the majority of the work sponsored by American Council of Learned Societies Committee on Native American Languages, which was directed by Franz Boas, Edward Sapir, Alfred Kroeber, and other academic linguists from 1927-1937. The collection, however, also contains related kinds of fieldwork and derived secondary materials created outside the auspices of this Committee, both earlier and later. The first deposit of the material arrivied in 1945. Subsequently, additional related materials were donated and added, as noted in the listings. Additionally, the documentary materials produced by some of the early projects (1945 to circa 1955) of the APS Phillips Fund for Native American Research were added to this collection. The collection has grown to over 80 linear feet of material representing at least 166 languages and dialects from the United States, Canada, and Mexico. The formats range from field notes and ethnographic texts to slip files, vocabularies, lexica, and grammars, and dozens of linguists and Native consultants are represented.