English academic and Roman Catholic priest Aidan Nichols wrote that "at root, only one issue of substance divides the Orthodox and the Catholic Churches, and that is the issue of the primacy." The French Orthodox researcher Jean-Claude Larchet wrote that together with the Filioque controversy, differences in interpretation of this doctrine have been and remain the primary causes of schism between the Roman Catholic Church and the Orthodox Church. In the Eastern Orthodox Churches, some understand the primacy of the Bishop of Rome to be merely one of greater honour, regarding him as primus inter pares ("first among equals"), without effective power over other churches. Other Orthodox Christian theologians, however, view primacy as authoritative power: the expression, manifestation and realization in one bishop of the power of all the bishops and of the unity of the Church.
The Roman Catholic Church attributes to the primacy of the Pope "full, supreme, and universal power over the whole Church, a power which he can always exercise unhindered," a power that it attributes also to the entire body of the bishops united with the pope. The power that it attributes to the pope's primatial authority has limitations that are official, legal, dogmatic, and practical.
In the Ravenna Document, issued in 2007, representatives of the Orthodox Church and the Roman Catholic Church jointly stated that both East and West accept the fact of the Bishop of Rome's primacy at the universal level, but that differences of understanding exist about how the primacy is to be exercised and about its scriptural and theological foundations.
The Roman Catholic dogma of the primacy of the bishop of Rome is codified in both codes of canon law of the Roman Catholic Church – the Latin Church's 1983 Code of Canon Law (1983 CIC) and the Eastern Catholic Churches' 1990 Code of Canons of the Eastern Churches (CCEO). The Second Vatican Council's 1964 dogmatic constitution Lumen gentium (LG) declared that the "pope's power of primacy" is by "virtue of his office, that is as Vicar of Christ and pastor of the whole Church," and is "full, supreme and universal power over the Church" which he "is always free to exercise." The primacy of the bishop of Rome, according to John Hardon in Catholic Dictionary, is "primacy of jurisdiction, which means the possession of full and supreme teaching, legislative, and sacerdotal powers in the Catholic Church"; it is authority "not only in faith and morals but Church discipline and in the government of the Church."
In 1983 CIC canon 331, the "bishop of Roman Church" is both the "vicar of Christ" and "pastor of the universal Church on earth." Knut Walf, in New commentary on the Code of Canon Law, notes that this description, "bishop of the Roman Church," is only found in this canon, and the term Roman pontiff is generally used in 1983 CIC. Ernest Caparros' et al. Code of Canon Law Annotated comments that this canon pertains to all individuals and groups of faithful within the Latin Church, of all rites and hierarchical ranks, "not only in matters of faith and morals but also in all that concerns the discipline and government of the Church throughout the whole world." Heinrich Denzinger, Peter Hünermann, et al. Enchiridion symbolorum (DH) states that Christ did not form the Church as several distinct communities, but unified through full communion with the bishop of Rome and profession of the same faith with the bishop of Rome.
The bishop of Rome is the supreme authority of the sui iuris Eastern Catholic Churches. In CCEO canon 45, the bishop of Rome has "by virtue of his office" both "power over the entire Church" and "primacy of ordinary power over all the eparchies and groupings of them" within each of the Eastern Catholic Churches. Through the office "of the supreme pastor of the Church," he is in communion with the other bishops and with the entire Church, and has the right to determines whether to exercise this authority either personally or collegially. This "primacy over the entire Church" includes primacy over Eastern Catholic patriarchs and eparchial bishops, over governance of institutes of consecrated life, and over judicial affairs.
Primacy of the bishop of Rome was also codified in the 1917 Code of Canon Law (1917 CIC) canons 218–221.