The N40 road is a national primary road in Cork City, Ireland. It is partial ring road skirting the southern suburbs of the city, from the N22 west of Ballincollig, via the Jack Lynch Tunnel under the River Lee, to the Dunkettle Interchange where it meets the N25 and N8/M8. The present N40 designation was created on 23 February 2012 via statutory instrument by renaming parts of the N22 and N25. The N40 serves as both a commuter route and a bypass of the city centre for traffic between parts southwest and east. The National Transport Strategy envisages building a "Cork North Ring Road" to complete the circuit in the 2030s.

A national primary road is a road classification in Ireland. National primary roads form the major routes between the major urban centres. There are 2649 km of national primary roads. This category of road has the prefix "N" followed by one or two digits. Motorways are prefixed "M" followed by one or two digits.