The first chapter provides a short survey of the language of joy as it is found in philosophical, theological and mystical works that have a strong bearing upon European medieval literature as a whole. It shows how some influential theoretical and mystical works shape a cognitive and conceptual language of joy as exterior to the self, a place of alterity that the human mind cannot contain within itself but must enter through love and self-forgetfulness. Through an exploration of some of the writings of St Augustine, Boethius, Thomas Aquinas and Bernard of Clairvaux, I argue that this language is constructed in opposition to that of philosophical happiness which consists in self-sufficiency and intellectual contemplation. The chapter ends with a study of the mystic Marguerite Porete’s language of divine union as an entering of the sea of joy, which blends the monastic and courtly discourses of love.