Plainchant is the oldest substantial body of music that has been preserved in any shape or form. It was first written down in Western Europe in the wake of the Carolingian renaissance of the 8th and 9th centuries. Many thousands of chants have been sung at different times or places in a multitude of forms and styles, responding to the differing needs of the church through the ages. This book provides a clear and concise introduction, designed both for those to whom the subject is new and those who require a reference work for advanced studies. It begins with an explanation of the liturgies which plainchant was designed to serve. All the chief genres of chant, different types of liturgical book, and plainchant notations are described. The later chapters are complemented by plates, with commentary and transcriptions. After an exposition of early medieval theoretical writing on plainchant, a historical survey follows the constantly changing nature of the repertory through from the earliest times to the restoration of medieval chant a century ago. The historical relations between Gregorian, Old-Roman, Milanese, Spanish, and other repertories is considered. Important musicians and centre of composition are discussed, together with the establishment of Gregorian chant in all the lands of medieval Europe, and the reformations and revisions carried out by the religious orders and the humanists. Copiously illustrated with over 200 musical examples transcribed from original sources, the book highlights the diversity of practice and richness of the chant repertory characteristic of the Middle Ages. As both a self-contained summary and also, with its many pointers to further reading, a handbook for research, it will become an indispensable reference book on this vast subject.