| Jurisdiction: | Mission sui iuris |
| Saint Helena, Ascension and Tristan da Cunha | |
| Latin: | Missio sui iuris Sanctae Helenae, Ascensionis et Tristanensis |
| Country: | Saint Helena, Ascension and Tristan da Cunha |
| Territory: | Saint Helena, Ascension and Tristan da Cunha |
| Province: | Immediately subject to the Holy See |
| Area Km2: | 308 |
| Population: | 5,500 |
| Population As Of: | 2017 |
| Catholics: | 200[1] |
| Catholics Percent: | 3.6 |
| Parishes: | 3 |
| Denomination: | Catholic Church |
| Sui Iuris Church: | Latin Church |
| Rite: | Roman Rite |
| Established: | 18 August 1986 |
| Priests: | 2 |
| Bishop: | Fr Tom Thomas Pattasseril IC |
| Bishop Title: | Superior |
| Suffragan: | for one --> |
| Archdeacon: | for one--> |
The Mission sui iuris of Saint Helena, Ascension and Tristan da Cunha (Latin: Missio sui iuris Sanctae Helenae, Ascensionis et Tristanensis) is part of the worldwide Catholic Church, under the spiritual leadership of the Pope in Rome. The Mission sui iuris is located in Saint Helena, Ascension and Tristan da Cunha and covering the Islands Saint Helena, Ascension and Tristan da Cunha.
There are three churches on the islands pertaining to the Catholic mission:
On August 18, 1986 the Mission sui iuris of Saint Helena, Ascension and Tristan da Cunha was established from the Archdiocese of Cape Town in South Africa. From the start, the office of its ecclesiastical superior (also exempt, i.e. immediately subject to the Holy See) has been vested in the Apostolic Prefecture of the Falkland Islands, another UK Southern Atlantic overseas possession.