A reflection on the idea of the "composer" in the medieval period, including a study of the individuals and groups active in the creation of medieval music. The modern concept of the individual composer is central to accounts of Western music, and continues to represent a critical field of research in musicology. However, this approach cannot be straightforwardly transposed to the Middle Ages, as it does not reflect the complex creative realities of medieval composition, and conflicts with the evidence from extant sources and documentation. This collection, the first full-length study of the subject, questions and revises the concept of the composer for the medieval period through five thematic parts: 'Historiographical Critique', 'Ascriptions, Attributions, Signatures', 'Medieval Constructions of Authority and of the Authorial Persona', 'The Composing Workshop', and 'Composers as Communities'. Spanning a period from the seventh century to the early Renaissance, and taking in different cultural and geographical areas of Western Europe, the essays examine a range of repertoires and fields - plainchant, Latin devotional song, medieval motet, trouvère song, Ars nova, drama, and illuminated Gothic manuscripts - in diverse contexts, from clerical communities, to princely courts and lay workshops. Overall, the new perspectives here shed fresh light on the musical practices and repertoires of the Middle Ages.