Canonical territory in canon law is the specifically defined geographic territory of an ecclesiastical entity, whether a diocese, archdiocese, autocephalous church, etc. Outside that territory, the authorities of that entity have no canonically ecclesiastical jurisdiction. This principle is based on the canons of the First Ecumenical Council, which do not permit overlapping jurisdiction to bishops.
The canonical territory of autocephalous and autonomous churches is usually defined by pan-Orthodox agreement, such as at an Ecumenical Council. The canonical territory of any internal structures within such churches is defined by the authorities of those churches themselves, usually the holy synod.
Since the 20th century, canonical territory has increasingly become a violated principle of canon law, as numerous churches now have parishes in the diaspora, the geographic territory outside the canonically defined boundaries of the autocephalous and autonomous Orthodox churches. The canons as they now exist do not directly address how churches may expand into new territory, but it is instead forbidden to ordain clergy to serve outside one's existing canonical territory. In addition, throughout the history of the Orthodox Church, violations against this principle have taken place, as bishops sometimes seek to interfere within the canonical territory of other bishops.