The Catalano-Genoese friendship was forged as a result of their joint struggle against Islam in the Xllth century and was maintained during the Xlllth century, in spite of the Catalan maritime expansion that might have become a rivalry for Genoa. The friendship and cooperation was made evident in the granting of commercial franchises to the Genoese who were trading in Catalonia and in the lands they subsequently conquered. Catalans, for their part, had the same commercial franchises in Genoa and in the districts under their control. The war of Genoa against Pisa led as a consequence to an increase of maritime conflict between Catalan and Genoese, especially during the two last decades of Xlllth century, due to the major presence of Catalans in the Pisan ports and the transport of goods for Pisa, at that moment when Genoa was trying to block Pisa. All during the reign of James II, the alienation of the two competitors grew until it led to war. All these points are analyzed in the article in the light of unpublished records.