This series consists of the professional, personal, and family correspondence of Frederick N. Knapp; correspondence of Henry B. Rogers; orders, vouchers, receipts, reports, printed matter, and other papers related to the U.S. Sanitary Commission; and newspaper clippings. Among the correspondents are J. B. Abbott, John A. Anderson, George A. Blake, John S. Blatchford, Emma J. Brintzinghoffer, John B. Burns, James Freeman Clarke, G. R. Davis, Darius Forbes, Elisha Harris, William A. Hovey, Julia McCarthy, Edward B. Northrop, Frederick Law Olmstead, Louise A. Webster, and many others, including soldiers and their families.

Knapp family members represented in this series include Knapp's wife Lucia (Bradford) Knapp, his brother Francis Bellows Knapp, his son Frederick Bradford Knapp, and his cousin Henry W. Bellows. The series also contains letters to "the soldiers' friend," Miss Amy M. Bradley; letters to Knapp's cousin Susan Newman Knapp; and correspondence between Knapp and Thomas Hill, his Harvard classmate and president of Harvard.

This series contains Frederick N. Knapp's unpublished manuscript on the work of the Special Relief Department, U.S. Sanitary Commission. The manuscript consists of draft pages describing various aspects of the Commission, including edits and annotations. Some portions are written in other hands, including J. B. Abbott's.

This series includes notes by Lucia (Bradford) Knapp on the life and work of her husband Frederick N. Knapp; unidentified miscellaneous notes on Civil War hospitals; and an undated manuscript containing copies of correspondence, extracts of reports, and other material related to Dr. George A. Blake and the work of the U.S. Sanitary Commission in Louisiana, Texas, and Alabama, 1862-1865. The manuscript is in Blake's handwriting, and a cover sheet includes the note: "Part used by Mr. Knapp."

This series consists of the Civil War diaries of Henry Bromfield Rogers, agent for the U.S. Sanitary Commission, documenting his work distributing supplies and providing assistance to soldiers. Included are observations of the sick and dying, names of wounded and discharged men, and descriptions of camp life and daily activities. The two draft volumes contain notes Rogers used to write fuller entries in the diaries.