“The Lay Faithful,” in The Catechism of the Catholic Church, par. 897-913.
Ecclesiae de Mysterio, “Instruction on Certain Questions Regarding the Collaboration of the Non-Ordained Faithful in the Sacred Ministry of Priests,” Congregation for the Doctrine of the Faith and other Vatican dicasteries (8/15/1997)
Pope John Paul II: “Post-Synodal Apostolic Exhortation: On the Vocation and Mission of the Lay Faithful in the Church and in the World,” Christifideles Laici (12/30/1988)
Pope Paul VI: "On the Celibacy of the Priest," Sacerdotalis Caelibatus (encyclical, 6/24/1967)
Pope John Paul II: “Post-Synodal Apostolic Exhortation: On the Formation of Priests in the Circumstances of the Present Day,” Pastores Dabo Vobis (3/25/1992)
Pope John Paul II: "Holy Thursday Letters to Priests"
Letters for some years are missing from the Vatican website (marked ? above).
For some other years, the Vatican website has the letter available in several languages, but not in English; the years listed in italics above link to the Spanish translations.
Pope John Paul II:Wednesday audience catechesis on the priesthood (1993) - available on the Vatican.va website in Italian (and sometimes also French and/or Spanish), but not in English
Vatican II: "Decree concerning the Pastoral Office of Bishops in the Church," Christus Dominus (10/28/1965)
Pope John Paul II: “Post-Synodal Apostolic Exhortation: On the Bishop, Servant of the Gospel of Jesus Christ for the Hope of the World,” Pastores Gregis (10/16/2003)