Ecclesiastical heraldry refers to the use of heraldry within Christianity for dioceses, organisations and Christian clergy. Initially used to mark documents, ecclesiastical heraldry evolved as a system for identifying people and dioceses. It is most formalized within the Catholic Church, where most bishops, including the Pope, have a personal coat of arms. Clergy in Anglican, Lutheran, Eastern Catholic and Eastern Orthodox churches follow similar customs, as do institutions such as schools and dioceses.
Ecclesiastical heraldry differs notably from other heraldry in the use of special insignia around the shield to indicate rank in a church or denomination. The most prominent of these insignia is the low crowned, wide brimmed ecclesiastical hat, commonly the Roman galero. The color and ornamentation of this hat indicate rank. Cardinals are famous for the "red hat", while other offices and churches have distinctive colors of hat, such as black for priests and green for bishops, customarily with a defined number of tassels that increases with rank.
Other insignia include the processional cross, and the episcopal mitre and crosier. Eastern traditions favor the use of their own style of hat and crosier, and the use of the mantle or cloak rather than the ecclesiastical hat. The motto and specific shapes of shields are more common in ecclesiastical heraldry, while supporters and crests are less common. The papal coats of arms have their own heraldic customs, primarily the papal tiara, the keys of Saint Peter, and the ombrellino (umbrella). Pope Benedict XVI substituted a specific design of mitre for the papal tiara in his coat of arms, being the first pope to do so, although Pope Paul VI was the last pope to be crowned with the papal tiara. The arms of ecclesiastical institutions have somewhat different customs, using the mitre and crozier more often than is found in personal arms, though different churches greatly vary in their use. The arms of corporations (organizations) are denominated "impersonal" or "corporate" arms.