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.

This is primarily a collection of letters, with some additional documents, concerning Young's interest in botany, geology, mineralogy, and natural history. There is information about Bowdoin College, where he studied under Parker Cleaveland. There is also much on the natural history of Maine, where he was the State Botanist in 1847-1849, and also on the Bangor Natural History Society. There are materials on Brazil in relation to Young's service there as the U.S. consul to Rio Grande do Sul from 1863 to 1873. There are also letters from his brother, John C. Young, and his sister, Sarah Augusta Young.