The numerous Latin and Greek letters written by the prolific Italian humanist Francesco Filelfo (1398-1481) not only grant us insight into Filelfo’s own intellectual endeavours and his frenetic literary journey between East and West. Addressed to the most prominent humanists, prelates and rulers of his age, the epistles, in which Filelfo so enthusiastically displays his erudition and ambition, are also an important source for early modern history. Spanning half a century, Filelfo’s letter collection is an idiosyncratic assemblage of diverse epistolary genres, juxtaposing short memos to close friends with lengthy and learned philosophical essays, warm recommendation letters with virulent pamphlets. Many letters move freely between subjects, intermingling practical matters, literary allusions, philological detail and caustic comment on contemporary politics. This critical edition of Filelfo’s complete canonical letter collection in forty-eight books offers historians as well as literary scholars access to Filelfo’s vast oeuvre, and through it to the multifaceted world of Quattrocento humanism. Documenting the various previous editorial stages that the epistolarium underwent, this edition of Filelfo’s Collected letters is primarily based on the final, authorised redaction as it is preserved in manuscript 873 of the Biblioteca Trivulziana in Milan, a collection of over two-thousand letters written between 1427 and 1477, established by Filelfo himself and transcribed under his supervision.