A co-cathedral is a cathedral church which shares the function of being a bishop's seat, or cathedra, with another cathedral, often in another city (usually a former see, anchor city of the metropolitan area or the civil capital). Instances of this occurred in England before the Protestant Reformation in the dioceses of 'Bath and Wells', and of 'Coventry and Lichfield'. These two dioceses were each named for both cities that served as bishop's seats.
Many are former cathedrals, but even if still in use, those often are not granted co-cathedral status.
Often the diocese with one or more co-cathedrals also has a multiple ("hyphenated") name reflecting these, but some have a co-cathedral not mentioned in the title while other former see titles may also be preserved without having a co-cathedral. Sometimes the first-named city does not have the main cathedral (actual see) but boasts another distinction such as being a national capital or having an august ecclesiastical past.