Langstone Harbour is an inlet of the English Channel in Hampshire, sandwiched between Portsea Island to the south and west, Hayling Island to the south and east, and Langstone to the north. Geographically it is a ria.
Together with Chichester Harbour, which is at the other (eastern) side of Hayling Island it is designated as a Special Protection Area for wildlife. West of Portsmouth is Portsmouth Harbour and the three linked harbours are important recreational and conservation areas as well as supporting commercial fishing and shipping. It is administered by the Langstone Harbour Board.
The eastern boundary with Chichester Harbour is defined by a historic causeway known as the wade way, which was originally the only crossing between Hayling Island and the mainland. It is now impassable, having been cut in two by a deep channel for the Portsmouth and Arundel Canal in the 1820s (for further information see Langstone).
Langstone Harbour contains a number of islands; Baker's Island (SU694035), North Binness Island (SU692046), South Binness Island (SU698031) and (SU701041). These are subject to erosion and during the 1990s a seven-year archaeology project took place before their history was lost to the seas.