Francis Thynne's Perfect Ambassadour, written in 1578, is the earliest surviving English treatise on the role of the ambassador. Thynne's conception of appropriate diplomatic activity was influenced by historical precedent. Thynne drew directly on ancient Greek and Roman authors; he also included information about classical and medieval diplomacy derived indirectly from more recent publications, such as Theodore Zwinger's Theatrum Vitae Humanae. After briefly outlining the content of the treatise, Tracey A. Sowerby assesses the significance of Thynne's method and explains what it tells us about the mediation of diplomatic knowledge. Sowerby then compares it to other early modern diplomatic treatises and Elizabethan ambassadors' understanding of their activities.