This is the first of a three-volume series dedicated to Dublin Castle and the archaeological excavations carried out there.Volume 1 presents a history of Dublin Castle, covering the period from the first Viking settlement in the ninth century to 1850. The castle was the center of English (and later British) royal government in Ireland from the 1170s until it was handed over to the Provisional Government of Ireland in 1922. A large early thirteenth-century castle, built on the orders of King John, stood on the site until it was gradually replaced between the 1680s and the 1770s by the present quadrangle of palatial buildings. The only intact portion of the medieval castle to survive this rebuilding is the large, circular south-east corner tower, known today as the Record Tower. It is the first substantial history of the castle to be published and is intended to provide a comprehensive historical background to the results of archaeological excavations undertaken between 1961 and 1987.