The General Manuscript Collection is an artificial collection of correspondence, diaries, lecture notes, class work, essays, administrative documents, minutes, and other documents collected by the Rare Book & Manuscript Library. Single items or very small collections are generally classified as part of the general manuscript collection rather than assigned an individual manuscript number. Additionally, small additions to existing RBML manuscript collections may be classified as part of the General Manuscript Collection.

Letters written to Gay from political and literary contemporaries such as Horace Greeley, Charles Sumner, and William Bryant; reports in letter form from his reporters at the front during the Civil War; and personal correspondence including many letters from his wife, Elizabeth Neall Gay. Letters written to Mrs. Gay from family friends and business associates including many from her husband. Correspondence of other members of the Gay family including Walter Gay, Sarah Gay, and Allan Gay. Diaries, notebooks, and journals of Sydney Howard Gay.