A concordat is a bilateral instrument of international law concluded between the Holy See, acting through its diplomatic personality, and a state. It typically governs matters where ecclesiastical and civil jurisdictions overlap: recognition of canonical marriage, religious education in public schools, the legal personality of dioceses and religious orders, tax treatment of Church property, appointment procedures for bishops, and chaplaincies in armed forces or prisons.
Concordats are treated as treaties under the Vienna Convention on the Law of Treaties, since the Holy See is a recognized subject of international law distinct from Vatican City State. They are negotiated by the Secretariat of State through the Section for Relations with States and are usually ratified following the receiving state's normal treaty procedures.
The form has medieval origins, with the Concordat of Worms (1122) settling the Investiture Controversy between Pope Calixtus II and Emperor Henry V. Modern landmark instruments include the Lateran Treaty of 1929 between the Holy See and Italy, which created Vatican City and resolved the Roman Question, and the Reichskonkordat of 1933 with Germany. Post-conciliar concordats, often called accords or agreements, tend to be narrower and more rights-based, reflecting Vatican II's stance on religious freedom in Dignitatis Humanae.
For diplomatic practitioners, concordats illustrate three features worth noting: (1) a non-territorial entity exercising full treaty-making capacity; (2) the use of treaty law to manage church-state relations rather than purely domestic legislation; and (3) the persistence of pre-Westphalian diplomatic forms within the modern system. Critics argue concordats can entrench privileges for one confession; defenders view them as predictable legal frameworks that protect religious minorities and clarify mutual obligations. Concordats may be revised, denounced, or supplemented by additional protocols, as occurred when Italy and the Holy See revised the Lateran arrangements through the Villa Madama Agreement in 1984.
Example
In 1984, Italy and the Holy See signed the Villa Madama Agreement, revising the 1929 Lateran Concordat and ending Catholicism's status as Italy's state religion.