The Institute of Christ the King Sovereign Priest, Latin: Institutum Christi Regis Summi Sacerdotis, abbreviated as ICRSS and ICKSP, is a society of apostolic life of pontifical right in communion with the Holy See of the Catholic Church. The institute has the stated goal of honouring God and the sanctification of priests in the service of the Catholic Church and souls. An integral part of the institute's charism is the use of the traditional liturgy, namely the Tridentine Missal for Mass, the Breviary of John XXIII for the Divine Office, and the Rituale Romanum for other sacraments. The society has undertaken the restoration of a number of historic church buildings.

Traditionalist Catholicism is a movement that emphasizes beliefs, practices, customs, traditions, liturgical forms, devotions and presentations of teaching associated with the Catholic Church before the Second Vatican Council (1962–1965). Traditionalist Catholics particularly emphasize the Tridentine Mass, the Roman Rite liturgy largely replaced in general use by the post-Second Vatican Council Mass of Paul VI.