The project "The European Dimension of a Group of Power: Ecclesiastics and the political State Building of the Iberian Monarchies (13th-15th centuries)” supported by the Fundação para a Ciência e Tecnologia assembled an inter-university team, that brought together researchers from five Portuguese universities and three Spanish universities, as well as consultants from three different universities. The book now being published is one of the outcomes of the work undertaken by the Iberian inter-university team. It confirms the possibilities opened up by teamwork and compared perspectives, as well as the need to pursue this approach in order to clarify the circumstances and conditionalities of a relationship from which both sides benefited. Thus the studies gathered here seek to return to the question of the Church's and clerics' contribution to the construction of royalty, approaching the peninsular context in a comparative way and analysing that contribution on different levels.