Western Sydney is a major region of Sydney, New South Wales, Australia. It has a number of different definitions, although the one consistently used is the region composed of the nine local government authorities which are all members of the Western Sydney Regional Organisation of Councils (WSROC).
Western Sydney as defined by the WSROC region covers 5,800 square kilometres (2,200 sq mi) and had an estimated resident population as at 30 June 2008 of 1,665,673. The region comprises the areas administered by the Blacktown City Council, Blue Mountains City Council, Canterbury-Bankstown Council, Cumberland Council, Fairfield City Council, Hawkesbury City Council, Liverpool City Council, City of Parramatta Council, and the Penrith City Council.
Western Sydney is also sometimes used to refer to the Greater Western Sydney region, which is the combination of Western Sydney as defined above and the Macarthur Region (also referred to as South-western Sydney). As well as the nine councils listed above, the GWS region includes Camden Council, Campbelltown City Council and Wollondilly Shire Council.
The NSW Government's Office of Western Sydney uses the broader Greater Western Sydney definition to refer to the region, which includes both WSROC and MACROC council areas.