This series contains two letterbooks of Jacob Wendell with manuscript copies of his outgoing business correspondence. Some letters are in Dutch. Included are letters of Wendell's nephew John after he joined the firm. The series also contains two letterbooks of Jacob Wendell & Sons with outgoing business correspondence, invoices, and accounts. Letters beginning in 1761 were written by Wendell's sons and business partners John Mico Wendell and Oliver Wendell. The fifth letterbook was kept by Oliver Wendell.

Among the many correspondents are consignees, ship captains, and others, including Francis Baker, Samuel Clarke, John Ellery, William Ellery, John Erving, Thomas Forster, Theodore Hodshon, William Hodshon, Phillip Livingston, Robert Livingston, James Oliver, Peter Oliver, Robert Sanders, and Samuel Storke. Some correspondents are family members, but letters relate primarily to Jacob Wendell's shipping business between the U.S., Europe, and the Caribbean, including trade in logwood, rice, sugar, molasses, rum, cotton, fish, and other cargo, as well as various financial matters. Also included are letters related to his efforts to ransom New England colonizers captured by Native Americans and taken to Canada in the 1720s; enslaved people he purchased and sold; his work on the Massachusetts Council; the illness and death of his oldest son Jacob, Jr. in 1753; enlistment and provisions for the French and Indian War and the Crown Point Expedition (Wendell served on the Committee of War); and the Boston fire of 1760.

The account books in this series include two volumes with correlating entries, both kept by Jacob Wendell: daily accounts and a ledger, 1708-1715. Other volumes kept by Jacob Wendell consist of daily accounts, 1731-1761; miscellaneous invoices and accounts; and accounts related to the frigate Massachusetts, with accounts and an inventory of the estate of Dorothy Jackson kept by Oliver Wendell. The collection also contains two volumes related to the estate of Edmund Quincy: a ledger of accounts and an alphabetical name index to the ledger; as well as a volume of daily expenses and cash accounts kept by Charles C. Foster. The Fosters were related to the Wendells through the Van Rensselaer family.