An instruction on certain matters to be observed or avoided regarding the Most Holy Eucharist, prepared at the request of John Paul II in Ecclesia de Eucharistia and given on the Solemnity of the Annunciation. Its eight chapters set out the regulation of the sacred liturgy, the participation proper to the lay faithful, the celebration of Mass and its parts, the distribution and reception of Holy Communion, other aspects of eucharistic worship including reservation and adoration, extraordinary functions of the lay faithful, and remedies for abuses — listing the graviora delicta and other grave matters and the right of the faithful to a liturgy celebrated according to the books.