Concept of canon; sacred canons of the first millennium as part of the common disciplinary heritage of all the Eastern Churches; the First Vatican Council on the codification of canon law of the Eastern Catholic Churches; the attempts in the aftermath of that Council; CIC-1917 and the Eastern Catholic Churches; Pius XI and the constitution of the Commission for the Codification of Eastern canon law; the work of the Commission; Pius XII and the partial promulgation of CICO; Vatican II and the codification of Eastern canon law; Paul VI institutes the Commission for the Revision of Eastern canon law; the work of the Revision Commission; John Paul the II and the promulgation of the Codex Canonum Ecclesiarum Orientalium on 18 October 1990.