Greater Western Sydney (GWS) is a large region of the metropolitan area of Greater Sydney, New South Wales (NSW), Australia that generally embraces the north-west, south-west, central-west, far western and the Blue Mountains sub-regions within Sydney's metropolitan area and encompasses 11 local government areas: Blacktown, Blue Mountains, Camden, Campbelltown, Cumberland, Fairfield, Hawkesbury, Liverpool, Parramatta, Penrith and Wollondilly. It includes Western Sydney, which has a number of different definitions, although the one consistently used is the region composed of ten local government authorities, most of which are members of the Western Sydney Regional Organisation of Councils (WSROC). The NSW Government's Office of Western Sydney calls the region "Greater Western Sydney".
Radiocarbon dating suggests human activity occurred in the Sydney metropolitan area from around 30,000 years ago. The Darug people lived in the area that was greater western Sydney before European settlement regarded the region as rich in food from the river and forests. Parramatta was founded in 1788, the same year as Sydney, making it the second oldest city in Australia. Opened in 1811, Parramatta Road, which navigates into the heart of greater western Sydney, is one of Sydney's oldest roads and Australia's first highway between two cities – Sydney central business district (CBD) and Parramatta, which is now the sixth largest business district in Australia. Rapid population increase after World War II saw the settlement of many ex-service men and migrants in the greater west, making it one of the most urbanised regions in the country and an area of growing national importance.