The A27 is a major road in England. It runs from its junction with the A36 at Whiteparish (near Salisbury) in the county of Wiltshire. It closely parallels the south coast, where it passes through West Sussex and terminates at Pevensey (near Eastbourne and Bexhill) in East Sussex.

Between Portsmouth and Lewes, it is one of the busiest trunk roads in the UK.

Historically, for longer distance movement along the south coast, the M25 in combination with the M2, M20, M23 / A23, A3 / A3(M) and M3 has provided an attractive alternative to the actual south coast route of A259, A27 and M27. In 2002 an offpeak journey between Margate and Southampton via the M25 was 2 hours 30 minutes, and via the coastal route using the A259, A27 and M27 was 3 hours 50 minutes. The reason why the coastal route is so much slower than the M25 alternative, is largley due to a series of bottlenecks on the A27. These include Chichester, Arundel, Worthing and East of Lewes.

Proposals to improve the Chichester by-pass are on hold.