This liturgical volume gathers the principal chants used in the Roman Catholic liturgy for Sundays and feast days and presents them according to the official Vatican edition of Gregorian chant. Prepared and arranged by the Benedictine monks of Solesmes, the book was intended as a practical resource for cantors, choirs and clergy responsible for singing the Mass and the Divine Office. The publication brings together musical notation, liturgical texts and rubrics that guide the performance of the chant tradition within the context of the Roman rite and reflects the scholarly work of the Solesmes community in restoring and transmitting Gregorian chant practice. / The volume assembles a comprehensive collection of chants used throughout the liturgical year and organizes them in a structure that corresponds to the celebration of the Mass and the Divine Office on Sundays and major feast days. The contents include the ordinary chants of the Mass, the chants associated with the canonical hours, seasonal material linked to the liturgical calendar and the repertory related to the veneration of saints. Musical notation accompanies the Latin texts and allows the book to function both as a practical chant book and as a reference for liturgical performance. The arrangement follows the tradition established by the Benedictine monks of Solesmes, whose editorial work sought to present the chant repertory in a form suitable for liturgical use and scholarly transmission within the Roman Catholic tradition.