Composed in Naples in the 1530s, Juan de Valdes’s Dialogo de la lengua occupies a special place in Spanish humanism, just as its author is widely acknowledged by Renaissance scholars as one of the most important intellectuals of 16th-century Western Europe. This edition reflects on the complex early history of the earliest extant primary text (MS 8629, held in the Spanish National Library), which is unanimously accepted as the most reliable of the three): whether or not it could have been copied in Valdes’s lifetime, how and when it reached Spain from Naples (where it was written), its real intended recipients, its circulation amongst a circle of Castilian friends, and how it managed to evade the ubiquitous eyes of the Inquisition.