The Eugene Mayer papers document the activities of Eugene Mayer, a merchant agent of Bavarian extraction, from 1818 to 1828. They contain correspondence, legal, and financial papers. The collection is organized into two series.

Series I. Business Papers contains correspondence, legal, and financial papers which provide an overall view of J. Webb & Company's shipping business and Mayer's activities as an overseas merchant agent. Also described is the development of conflicts between John Webb and his American-based partner, Adrian Rancher, and the background and proceedings of a slander case brought against Charles Notari, a Salem resident and former company employee.

The correspondence consists of letterbooks, correspondence from J. Webb & Company, and letters from international merchants. The letterbooks contain Mayer's letters to J. Webb & Company, merchant correspondence, and copies of Notari's slanderous letters. Also included is 1825 correspondence regarding suspicions of Mayer's possible embezzlement of funds from a former employer. Occasional shipping accounts may be found throughout the letterbooks, most notably for the brig Orbit and the brig Malay. The John Webb & Company correspondence contains letters from the company's main office in Leghorn, from Frederick Barker, head of the firm's Genoese branch, and occasional business notes from Edward Mayer, Eugene's brother and a firm partner. The correspondence covers a wide variety of business activities and issues, including: letters describing market conditions, instructions for Mayer, letters of introduction, descriptions of Lewis Giunti & Company (a firm subsidiary near Florence which manufactured straw hats), and an enumeration of the charges and legal case against Charles Notari. Also of interest are a number of admonitory letters from John Webb regarding Mayer's conduct as the firm's American agent. The merchant correspondence contains letters from firms in Prato, Genoa, Livorno, Le Havre, Mexico, Halifax, Philadelphia, Providence, Boston, Baltimore, Belfast (Me.), and Salem.

The Webb and Rancher partnership papers illuminate the conflicts which developed between John Webb and his partner, Adrian Rancher. Included are the 1818 partnership agreement between Webb and Rancher (et. al.), correspondence from Rancher, and letters regarding the Webb-Rancher liaison (which included Rancher's rescue from European prisons in the 1810s and 1820s).

The bulk of the legal papers were generated by the Charles Notari slander case. The financial papers include prices current of J. Webb Company and other Italian firms, and Mayer's agent and household accounts.

Series II. Personal Papers contains correspondence and miscellaneous papers. The correspondence includes letters in English, French, Italian, and German from friends, Mayer's parents Benoit Jacques and Caroline Mayer, and his brothers Ricco and Edward. The family letters convey personal news, such as the death of B. J. Mayer in 1827, and discuss Eugene's professional conduct in the Notari slander case and his handling of his business contacts in America. Also included is correspondence regarding a new type of telescope and an Italian dance instructor who conducted classes in Boston, The miscellaneous papers include an 1821 essay on family life (in French), calling and trade cards, poetry, a printed sermon (undated), and notes on the economy of the Netherlands.