Chiefly correspondence with Alexander John Gaspard Marcet on chemistry, with references to Sir Joseph Banks, Jean Francois Berger, Johan Jakob Berzelius, Jean-Baptiste Biot, and others; a few letters to and from John Bostock, Thomas Cooper, John Wilson Croker, Giovanni Fabbroni, and Henry Penneck.

This collection is comprised of materials from seven repositories and includes correspondence from Banks' colleagues and explorers, such as John Hope, Josiah Wedgwood, Georg Forster, and Captain William Bligh; records of expenses for voyages and journeys; and journals kept during voyages to New Foundland and Labrador (1766) and around the world with Captain James Cook (1768-1771). Topics include botany and horticulture, marine life, and collecting specimens.

This collection includes letters from, and drafts of letters to, scientists, artists, musicians, soldiers, political figures, and court personages throughout Europe, especially Italy and France. Topics covered range from personal and social affairs to agriculture, botany, geology, natural history, coinage, museum management, politics, weights and measures, current affairs. The collection also includes four diaries, housed separately with manuscript volumes.

This collection consists of facsimiles of documents, microfilmed for "Philip Mazzei: the comprehensive microform edition of his papers, 1730-1816" (Kraus International Publications, 1982), and also typescripts and translations into English of other documents.