The chapter addresses the works of the major defender of the conciliarism of the Council of Basel: John of Segovia. John was notable for the profundity of his thought: he addressed fundamental concepts, including the nature of authority, the role of trust and the idea that ultimately only the truth has authority. In contrast there are considered the works of John of Turrecremata who provided the most important defence of he papalist position – the greatest work of ecclesiology of the late Middle Ages. This chapter also considers the works of Antonio de' Roselli – these showed clearly the difficulties involved in applying modern notions of conciliarism and papalism in attempting to understand the thought of this period. The chapter ends with an evaluation of conciliarism. This shows that it was overwhelmingly a scholastic and clerical movement; that it was not as radical as it might appear.