The A40 is a trunk road which runs between London and Goodwick (Fishguard), Wales, and officially called The London to Fishguard Trunk Road (A40) in all legal documents and Acts. Much of its length within England has been superseded by motorways, such as the M40, and has lost its trunk road status, though it retains it west of Gloucester, including its length within Wales. It is approximately 260 miles (420 km) long. The eastern section from Denham, Buckinghamshire to Wheatley, Oxfordshire is better served by the M40 and its former function of linking London with Cheltenham and Gloucester has been taken by the M4, A419 and A417 via Swindon.

Fishguard is a coastal town in Pembrokeshire, Wales, with a population of 3,400 as of the 2021 census. Modern Fishguard consists of two parts, Lower Fishguard and the "Main Town". Fishguard and Goodwick are twin towns with a joint Town Council.