• The Bugnini-Liturgy and the Reform of the Reform by László Dobszay (2003): the renowned liturgical scholar reviews the ritual changes propulgated by Pope Paul VI, discusses the state of church music, and considers the possibility of a “reform of the reform”.
• Catholic Church Music by Richard Terry (1907): this guide by the organist of Westminster Cathedral records the musical and ritual practice of his era.
• Chants of the Vatican Gradual (1934) by Dominic Johner, OSB [two missing pages of above PDF here]: a musical and spiritual commentary on the chants for the Sundays and major feasts of the year.
• Crux et Cithara, ed. Robert Skeris (1983): a collection of essays in honor of the German priest, theologian, and church musician Johannes Overath
• Cum Angelis Canere: A Festschrift for Richard J. Schuler, edited by Robert Skeris: essays in honor of the Minnesota pastor and long-time editor of Sacred Music
• Frequently Asked Questions on Sacred Music
• The Musical Shape of the Liturgy by Dr. William Mahrt: the Stanford professor of medieval and early modern music, an expert on performance practice, opens up the deep relation between the Roman liturgy and its characteristic music, Gregorian chant.
• Sing Like a Catholic by Jeffrey Tucker: essays on the revival of sacred music in present-day parishes
• The Spirit of Gregorian Chant by Marie Pierik (1939): a small book but wide-ranging, with chapters on history, notation, word, rhythm, liturgy, melody, and musicians.

• Catholic Church Music, by Richard Terry (1907): this guide by the organist of Westminster Cathedral records the musical and ritual practice of his era.
• 24 Frequently Asked Questions on Sacred Music
• Music rubrics for high Mass (1962 Missal)
• Music rubrics for low Mass (1962 Missal)
• One page description of musical rubrics for the EF Mass (1961)
• Psallite Sapienter: A Musician’s Guide to the 1962 Missal: organist B. Andrew Mills guides musicians through the classic form of the Roman Rite
• Rules Governing Chant: an excerpt from the Liber Usualis

• Pope Francis’ address to the Italian Saint Cecilia Association (2019)
• Chirograph on Sacred Music (Pope John Paul II, 2003), on the 100th anniversary of Pius X’s Tra le sollecitudini
• Letter to Artists (Pope John Paul II, 1999)
• Ordo Cantus Officii (1983): music rubrics for the Liturgy of the Hours
• Ordo Cantus Missae introduction: an unofficial translation of the Latin introduction to the 1974 Graduale Romanum and the Ordo Cantus Missae
• Voluntati Obsequens (1974), a letter to bishops from the Sacred Congregation for Divine Worship on the publication of Jubilate Deo as a minimum repertoire of plainchant
• Musicam Sacram (1967), musical principles for the implementation of the liturgical reform (from the Sacred Congregation of Rites, English translation)
• Musicam Sacram (1967) in Latin
• De musica sacra et sacra liturgia: (Latin, 1958): rubrics to encourage the sung Mass and implement the encyclical Musicae Sacrae of Pius XII
• De musica sacra et sacra liturgia (English translation, 1958)
• Musicae Sacrae, the encyclical of Pius XII on sacred music (1955)
• Tra le sollecitudini (1903): the groundbreaking letter of Pope Pius X that started a century of development in the Church’s approach to sacred music

• General Instruction of the Roman Missal (2011)
• General Instruction of the Roman Missal (2003)
• Missale Romanum (1920)
• Missale Romanum (1962)
• Sacrosanctum Concilium (Vatican II, 1963)
• Summorum Pontificum (Pope Benedict XVI, 2007)

• Sacred Music Journal Archives
• “Our Position” (1904): Raphael Molitor OSB (Beuron) on the value of the Vatican edition of plainchant
• Sacred Music and Liturgy Reform (1966/69)
• Gregorian Chant, The Greatest Unison Music, by Mother Georgia Stevens, director of the Pius X School of Liturgical Music
• From the St. Gregory Society:
  • Documents on Papal Legislation on Music (1947)
  • “The White List” of Approved and Recommended Music 1947 
  • “The Black List” of “disapproved music” (1922)
• Copyright information for the Liber and Graduale

Hidden Treasure: Can the Church recover her musical heritage? by Susan Benofy (at adoremus.org): an introduction to the Church’s 20th-century teaching documents on music

The Proper Chants of the Paschal Triduum by Mark Daniel Kirby, OSB