This volume presents the first edition and translation of the Dyalogus de potentia summi pontifices, a little known, fragmentary work of fourteenth-century political theory by the Dominican Dondinus of Pavia. Dedicated to the Avignon Pope John XXII (1316-1334), it provides theological, philosophical, and historical justifications for the spiritual and temporal supremacy of the papacy asserted by Boniface VIII in Unam Sanctam of 1302. The dialogue unfolds in a dream vision in which an apologist for papal power and a sceptic argue before a judge. While the text at points characterizes opponents of papal power as heretics and even seems to counsel violence against them, the sceptic in the dialogue is nonetheless characterized as sympathetic, reasonable, and open to persuasion. An extensive introduction by the editor relates the Dyalogus to relevant landmarks of intellectual history of the early fourteenth century (such as John XXII's constitution Si fratrum on the vacant Empire and the subsequent pamphlet war with the imperial claimant Ludwig of Bavaria, or the curial trial of secular university master John of Pouilly over his critique of papally-granted pastoral privileges for mendicant friars). The introduction also provides a precise political context for understanding the work through a reconstruction of the career of the author's patron, Cardinal Luke Fieschi of Genoa, and through a consideration of John XXII's pro-Angevin strategy of pacification, inquisition, and crusade against Ghibelline lords of Northern Italy like the Visconti of Milan. An apparatus fontium points out parallels in contemporary authors such as John of Paris, Giles of Rome, James of Viterbo, Dante, Ptolemy of Lucca, and Marsilius of Padua. This editorial work ultimately reveals how Dondinus of Pavia used prior papal apologia to construct a dialogue that was most likely intended as a didactic tool of political catechesis for a lay audience.