The Catholic Church is divided into different territories and sections. A definite territorial division that has been assigned its own church (that is, a local church) makes up a parish.
In the parish, the baptized faithful are guided by a pastor who is charged with attending to their sacramental, spiritual, and doctrinal needs. There are two types of parishes: national and territorial. Territorial parishes are assigned by land divisions, and national parishes by ethnicity.
For example, in a city there may be ten Catholic parishes. Out of the ten, five might be national. Anyone in that city can join the ethnic parish, provided they are of that ethnic makeup. Otherwise a person is assigned to a parish in the geographical area in which they live. Today the rules have relaxed a bit, and many national parishes might have different ethnic backgrounds instead of only one. Also, people may join other parishes outside their boundaries provided the pastor permits.
Together parishes make up a diocese. A diocese is also a territorial division, usually defined by counties. Pastors, priests, deacons, diocesan, and clerical religious administrators report to a bishop, who is the head of the diocese. The chancery office is command central for the diocese, and these offices contain the bishop, vicar general, judicial vicar, and all other departments. This office deals with matters pertaining to the clergy and the faithful of the diocese.
An archdiocese is basically a diocese, but of a great city and territory. Usually an archdiocese is also a metropolitan see, in which the archbishop is the “metropolitan” of a district of dioceses. (The term “metropolitan” is used for both the district and the archbishop at the head of it.) A metropolitan has certain distinctions.
First, when the dioceses in his metropolitan go to Rome for their “Ad Limina” visit, the metropolitan archbishop has special honors and is the first to see the pope. Second, a metropolitan can oversee a suffragan see if there is a problem. Finally, metropolitan archbishops tend to be elevated to a cardinal. Diocese and archdiocese can have auxiliary bishops assigned to help the ordinary. An eparchy is a diocese for Eastern Catholics. It denotes an ecclesiastical province. The official head of an eparchy is an eparch who is the local ordinary bishop.
All the dioceses and archdioceses of a certain country make up an Episcopal Conference. The Episcopal Conferences sponsor the National Conference of Bishops. As a whole, they decide upon rules and regulations concerning Catholics in their conference, they can make joint statements, and when the Pope leaves matters to be decided regionally, they can act and make decisions with the final approval from the Holy See.
Episcopal Conferences from all over the world make up the Universal Church in which the pope is the head, as Vicar of Christ. The pope is also the head of state. Vatican City is a separate country from Italy. It has its own coins, stamps, police, and government. As head of state, the Pope is the sovereign and has diplomatic immunity.
Like other countries, the Vatican has a diplomatic corps all over the world. The official name for an ambassador of the Holy See is an apostolic nuncio.