The A25 is the name given to the sections of the main route connecting Strangford with Castleblayney that lie in Northern Ireland.
The route has strategic importance, as it connects Downpatrick, Newcastle and Castlewellan with Newry, and thus provides a link with Dublin.
Between Castlewellan and Newry, the route passes through rural villages such as Kilcoo and Rathfriland, which would be considered part of the Mourne Country, due to their proximity to the mountains of the same name.
The junction between the two routes is currently being upgraded to have motorway characteristics as part of Newry's new bypass scheme (from Cloghoge Roundabout to the Belfast Road).
On the western side of the city, the road becomes the principal transport corridor serving much of south Armagh; running near Bessbrook, through Camlough, Belleek and Newtownhamilton.