The social, religious and linguistic history of medieval Sicily is both intriguing and complex. For several centuries prior to the Muslim invasion of 827, the Christian islanders had spoken dialects of either Latin or Greek. On the arrival of the Normans around the year 1060, Arabic was the dominant language and Islam the dominant religion. But by 1250, Sicily was again almost exclusively Christian with the Romance dialects of more recent settlers in evidence everywhere. Of particular importance was the formative period of Norman rule (1061-1194), when most of the key transitions from an Arabic-speaking, Muslim island, to a 'Latin'-speaking Christian one were made. This work sets out the evidence for those fundamental shifts and provides an authoritative framework for establishing the conventional thinking on the subject.