The Pisan scholar Hugh Eteriano was adviser on western church affairs to Manuel Comnenus, and lived in Constantinople from c.1165 -82, where he encountered an heretical group among the western inhabitants of the city, which prompted him to write the Contra Patarenos. Patarenes was an alternative name for Cathars, and this text is of considerable importance to an understanding of the relationship between the western Cathars and older Byzantine dualist movements. Hugh's treatise is here published for the first time in a text established from the two extant manuscripts, together with a commentary and translation, a biography of the author and an historical introduction about the place of Hugh's treatise in the history of Christian dualism.