Giles of Rome - Aegidius or Egidius Romanus, surnamed Colonna - combined several roles in his distinguished career: senior ecclesiastic, prolific author and commentator, university teacher and political theorist. It is under this last aspect that we are concerned with him. He produced two essays in political analysis: a treatise called "De regimine principum", completed in about 1280, and this work - "On Ecclesiastical Power". "Giles of Rome"s "On Ecclesiastical Power," is a discourse on there lation ship between royal (secular) and papal (spiritual) power, which represents a full exposition of the papal point of view. R.W.Dyson presents here a careful edition and facing-page translation of this important text in the history of political thought." Joel Kaye, Barnard College