This is a study of Layamon’s poem Brut . The author begins with an investigation into the English poet’s handling of his main source, Wace’s Roman de Brut , to determine what principles guided his own composition. These established, she goes on to distinguish between different sorts of variation from the Roman de Brut , thereby providing norms against which to gauge the probability of further, secondary sources. These additional sources are then identified in the various fields suggested by the poem: historical, literary, religious writings (or tales) in Welsh, English, French, Latin and perhaps even Scandinavian. This book is part of a series of works on Arthurian literature.