This handbook, in five volumes, represents a complete course of liturgical studies which the Pontifical Liturgical Institute offers to professors and students of liturgy in universities and seminaries and to other persons engaged in liturgical ministry. It is offered as model, source, and reference. This volume aims not only to contribute to the ongoing reflection on the meaning and purpose of the eucharist but also to offer to teachers and students of liturgy a handbook for studying the subject according to a system which is based on historical development, theology and doctrine, liturgical texts and traditions in both East and West, and pastoral considerations.