Seaforth is a suburb of northern Sydney, in the state of New South Wales, Australia. Seaforth is located 12 kilometres north-east of the Sydney central business district in the local government area of Northern Beaches Council and is part of the Northern Beaches region.
Seaforth overlooks Middle Harbour and is linked south to Mosman by the Spit Bridge. To the west, Seaforth overlooks Sugarloaf Bay across to the suburbs of Northbridge, Castlecrag and Castle Cove. The Garigal National Park sits on the northern border.