This book offers an integrated study of the English princess and Castilian queen Catherine of Lancaster (1373-1418), drawing on available archival, architectural, and poetic sources in England and Spain. Catherine s mother, Queen of Castile in exile, and father, the powerful military commander John of Gaunt, raised her to take the Castilian throne. This volume connects Catherine s early life, providing insights into those who promoted her cause from birth as Princess of Castile, and her later life as Princess of Asturias, then Queen-consort, and finally Dowager and Co-regent of Castile. Her influence on the Castilian court s poetic circles has not previously been connected to her English heritage. Poetry written about her and influenced by her was compiled into a songbook presented to her son, Juan II. The book brings new understanding of the role an Englishwoman played in Trastámara Castile s turbulent history.