The A3 is a route designation of a major metropolitan arterial route through suburban Sydney, connecting the A8 at Mona Vale at its northern end, to Princes Highway at Blakehurst at its southern end. This name covers a few consecutive roads and is widely known to most drivers, but the entire allocation is also known – and signposted – by the names of its constituent parts: Mona Vale Road, Ryde Road, Lane Cove Road, Devlin Street, Church Street, Concord Road, Homebush Bay Drive, Centenary Drive, Roberts Road, Wiley Avenue and King Georges Road.

Mona Vale is a suburb of Sydney, in the state of New South Wales, Australia. It is located 28 kilometres north of the Sydney central business district, in an area known as the Northern Beaches. Formerly the administrative centre of Pittwater Council, it is now located in the local government area of Northern Beaches Council. The traditional custodians of the area are the Garigal people. It is often colloquially referred to as "Mona".