This chapter examines the western reception of the creed and canons of the 325 Council of Nicaea. The Nicene–Constantinopolitan Creed appeared in the eucharistic liturgy towards the end of the sixth century, controversially with the insertion of filioque possibly at the Third Synod of Toledo in 589, although the creed was not used in Rome until 1014 under Benedict VIII, despite efforts by Charlemagne with Leo III early in the ninth century. The theological dispute over filioque resulted in the schism between East and West in 1054. The reception of the twenty canons of Nicaea as disciplinary law can be traced through letters of Roman bishops from the end of the fourth century onwards preserved mainly in what would become known as decretal collections. In the middle of the fourth century in Rome the canons from the 343 Synod of Serdica were conflated with the canons from Nicaea and early in the fifth century under Zosimus they were significant in the dispute between Rome and Carthage over questions of Rome’s authority. The questions examined are the degree to which the Catholic Church has considered the canons from Nicaea to be infallible and their status today.