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".

Sydney is the capital city of the state of New South Wales and the most populous city in Australia. Located on Australia's east coast, the metropolis surrounds Sydney Harbour and extends about 80 km from the Pacific Ocean in the east to the Blue Mountains in the west, and about 80 km from the Ku-ring-gai Chase National Park and the Hawkesbury River in the north and north-west, to the Royal National Park and Macarthur in the south and south-west. Greater Sydney consists of 658 suburbs, spread across 33 local government areas. Residents of the city are colloquially known as "Sydneysiders". The estimated population in June 2023 was 5,450,496, which is about 66% of the state's population. The city's nicknames include the "Emerald City" and the "Harbour City".