The A23 road is a major road in the United Kingdom between London and Brighton, East Sussex, England. It is managed by Transport for London for the section inside the Greater London boundary, Surrey County Council and West Sussex County Council for the section shadowed by the M23 motorway, National Highways between the M23 and Patcham, and by Brighton and Hove Council from the A27 to the centre of Brighton.

East Sussex is a ceremonial county in South East England. It is bordered by Kent to the north-east, West Sussex to the west, Surrey to the north-west, and the English Channel to the south. The largest settlement is the city of Brighton and Hove, and the county town is Lewes.