This book is intended as an introduction to the principal forms and orders of Western liturgy between about 900 and 1700, to explain their nature and basic historical origin, and to present in detail the contents and orders of principal services as well as additional and special forms of worship. The book emphasizes the mainstream of Western liturgy derived from the medieval Roman Rite as found in secular and monastic churches. After the Reformation it concentrates on the rites of the Roman Catholic Church and the Church of England. There is consideration of the nature of liturgy, a historical summary, and individual chapters on medieval churches and their communities, the Christian calendar, medieval liturgical books, the Psalms, the Office, the Mass, Processions and Additional Observances, Holy Week and Easter, the Tridentine Rite, and the English Book of Common Prayer. There are two further chapters which raise the problems of establishing the order of a liturgical service, and introduce selected medieval sources accessible in facsimile or edition. A select, annotated bibliography and a glossary of ecclesiastical and liturgical terms are included.