Sydney Harbour National Park is a national park comprising parts of Sydney Harbour, its foreshores and various islands. The park lies within the Sydney metropolitan area and was created in piecemeal fashion during the 20th century. Much of the harbour foreshores had been spoiled by residential development; what remained was preserved partly because of the presence of military bases, and partly because of the work of conservationists. Early precursors of today's "Greens" were responsible for stopping mining at Ashton Park in the 19th Century. Other places were saved because of people such as the visionary Neil Nielsen, who became the New South Wales Minister for Lands and a strong advocate of a public reserve around Sydney Harbour.

Nielsen was ahead of his time when he used the phrase "national park" in regard to the harbour foreshores, but Sydney eventually caught up with him. It was not possible to undo all the damage done in past decades, but there was still much that could be preserved, and the 1960s were a particularly active time in this regard. The New South Wales Government began buying land around the foreshores in 1965, and the National Trust suggested a national park in 1968. In the following year, the State Government announced a plan whereby it would buy Commonwealth land around the harbour. The Sydney Hartbour National Park was finally gazetted in 1975, with Nielsen Park at Shark Bay being added in 1978. Extra land was transferred from Commonwealth to State Government control, and added to the national park in 1979; the historically important quarantine station at Manly was added in 1984.