A concordat is an agreement between the Holy See of the Catholic Church and a sovereign state on religious matters. Legally, they are international treaties. They often includes both recognition and privileges for the Catholic Church in a particular country. Privileges might include exemptions from certain legal matters and processes, and issues such as taxation as well as the right of a state to influence the selection of bishops within its territory.^{[citation needed]}

The Council of Constance proclaimed the Concordat to be the regular form of governing relations between the Papacy and foreign kingdoms.^{[citation needed]}

Although for a time after the Second Vatican Council, which ended in 1965, the term 'concordat' was dropped, it reappeared with the Polish Concordat of 1993 and the Portuguese Concordat of 2004. A different model of relations between the Vatican and various states is still evolving (see e.g. Petkoff 2007) in the wake of the Second Vatican Council's Declaration on Religious Liberty, Dignitatis Humanae.^{[citation needed]}

The Venerable Pope Pius XII (Latin: Pius PP. XII; Italian: Pio XII), born Eugenio Marìa Giuseppe Giovanni Pacelli (2 March 1876 – 9 October 1958), reigned as Pope, head of the Catholic Church and sovereign of Vatican City State, from 2 March 1939 until his death in 1958.

Before election to the papacy, Pacelli served as secretary of the Department of Extraordinary Ecclesiastical Affairs, papal nuncio and Cardinal Secretary of State, in which capacity he worked to conclude treaties with European and Latin American nations, most notably the Reichskonkordat with Nazi Germany. The concordat of 1933 which saw the self-destruction of the Centre (Catholic) Party, on the orders of the Holy See, and Pius' leadership of the Catholic Church during World War II, including his "decision to stay silent in public about the fate of the Jews", remain the subject of controversy.

After the war Pius XII advocated peace and reconciliation, including lenient policies towards Axis and Axis-satellite nations. The Church experienced severe persecution and mass deportations of Catholic clergy in the Eastern Bloc. In light of his overt involvement in Italian politics – anyone who voted for a Communist candidate in the 1948 elections was threatened with automatic excommunication – Pius XII became known as a staunch opponent of the Italian Communist Party. Pius XII explicitly invoked ex cathedra papal infallibility with the dogma of the Assumption of Mary in his 1950 Apostolic constitution Munificentissimus Deus. His magisterium includes almost 1,000 addresses and radio broadcasts. His forty-one encyclicals include Mystici Corporis, the Church as the Body of Christ; Mediator Dei on liturgy reform; and Humani generis on the Church's positions on theology and evolution. He eliminated the Italian majority in the College of Cardinals in 1946.