The Diocese of Sessa Aurunca (Latin: Dioecesis Suessana) is a Latin diocese of the Catholic Church in southern Italy. Since 1979 it has been a suffragan of the Archdiocese of Naples.
 The inhabitants of Sessa Aurunca venerate as patron saint their Bishop, St. Castus, a martyr at the end of the third century. Scholars, however, reject the notion that he was a bishop of Sessa. There still remain ruins of the ancient basilica dedicated to him, with which catacombs are still connected.   The first bishop of certain date was Fortunatus (499); but until the end of the tenth century the names of the bishops are unknown.
 It is likely that Sessa Aurunca became the suffragan (subordinate) of Capua, when that diocese was raised to metropolitan status in 966 by Pope John XIII. It was certainly the case in March 1032, however, when Archbishop Atenulf of Capua consecrated Bishop Benedict of Sessa Aurunca, and confirmed him in the possession of the diocese, just as his predecessors had done. In the twelfth century, under the Normans,  Suessa was part of the ecclesiastical province of Capua.  The new cathedral was consecrated in 1113.
 The ancient cathedral of Sessa, dedicated to the Virgin Mary, was outside the city, next to the walls. In 1113 the seat of the bishop was transferred to a new cathedral in the center of the city, which was dedicated on 14 July to the Virgin Mary and Saint Peter.
 The cathedral is staffed and administered by a corporation, the Chapter, which is composed of four dignities (the Archdeacon, the Dean, and two Primicerii) and sixteen Canons. In 1757, there were twenty-five Canons.
 Following the extinction of the Napoleonic Kingdom of Italy, the Congress of Vienna authorized the restoration of the Papal States and the Kingdom of Naples. Since the French occupation had seen the abolition of many Church institutions in the Kingdom, as well as the confiscation of most Church property and resources, it was imperative that Pope Pius VII and King Ferdinand IV reach agreement on restoration and restitution. Ferdinand, however, was not prepared to accept the pre-Napoleonic situation, in which Naples was a feudal subject of the papacy. Lengthy, detailed, and acrimonious negotiations ensued.
 In 1818, a new concordat with the Kingdom of the Two Sicilies committed the pope to the suppression of more than fifty small dioceses in the kingdom. The ecclesiastical province of Naples was spared from any suppressions, but the province of Capua was affected. Pope Pius VII, in the bull "De Utiliori" of 27 June 1818, chose to suppress the diocese of Carinola (which is only five miles from Sessa) completely, and assign its people and territory to the diocese of Sessa.  In the same concordat, the King was confirmed in the right to nominate candidates for vacant bishoprics, subject to the approval of the pope. That situation persisted down until the final overthrow of the Bourbon monarchy in 1860.
 Following the Second Vatican Council, and in accordance with the norms laid out in the Council's decree, Christus Dominus chapter 40, major changes were made in the ecclesiastical administrative structure of southern Italy.  Wide consultations had taken place with the bishops and other prelates who would be affected. Action, however, was deferred, first by the death of Pope Paul VI on 6 August 1978, then the death of Pope John Paul I on 28 September 1978, and the election of Pope John Paul II on 16 October 1978. Pope John Paul II issued a decree, "Quamquam Ecclesia," on 30 April 1979, ordering the changes. Three ecclesiastical provinces were abolished entirely: those of Conza, Capua, and Sorrento. A new ecclesiastical province was created, to be called the Regio Campana, whose Metropolitan was the Archbishop of Naples. The dioceses formerly members of the suppressed Province of Capua (Gaeta, Calvi and Teano, Caserta, and Sessa Arunca) became suffragans of Naples.
 41°14′00″N 13°56′00″E﻿ / ﻿41.2333°N 13.9333°E﻿ / 41.2333; 13.9333