Casula is a suburb in the Sydney metropolitan area in the State of New South Wales, Australia. It is located approximately 35 kilometres (22 miles) south-west of central Sydney on the Hume Highway. The suburb of Casula is situated entirely within the Local Government Area of the City of Liverpool. Casula is the first suburb immediately south of Liverpool's city centre on the Hume Highway and the Main Southern Railway between Sydney and Melbourne.

Casula is well serviced by transport facilities. The suburb is bordered on the north and west by the M5 South-Western Motorway, with continuous freeway-standard highway to central Sydney and the North Shore. There is also a railway station serviced by CityRail, but not all trains stop there. The station is isolated and perceived to be unsafe (particularly for lone passengers and women). It is not served by bus transport. Relatively frequent bus services link Casula to the major commercial and retail centre of Liverpool and its major railway station.

Casula consists of undulating, gently rolling land, with elevations across the suburb being mostly between 30 and 70 metres above sea level. However, the Georges River forms the eastern boundary of the suburb, and its western bank is paralleled by a relatively steep escarpment.

Casula was first settled by agriculturalists in the nineteenth century, among them Richard Guise, who named his farm "Casula". The area became dominated by poultry farming, market gardening and fruit growing.

During the First World War, a large Australian Imperial Forces recruitment and training reserve was located in Casula - a fact reflected by the name of one of its major residential streets, "Reserve Road". This camp became briefly notorious in 1916 when a large mob of soldiers rebelled against the strict training regimen, marched on nearby Liverpool, ransacked and looted several pubs, hijacked several trains to Central Station in Sydney and continued their drunken rioting, resulting in the Military Police shooting dead one rioter.

Casula is notable for its variable demographics and mixture of socio_economic levels existing side by side. The area did not become suburbanised until the late 1950s when the first Housing Commission estates were built in the north of the suburb in the vicinity of the Hume Highway. Casula Primary School was opened on De Meyrick Avenue in 1959, and Casula High School was commissioned around 1973. Most of the central and southern portions were subdivided and developed over the next few decades, and even now there are pockets of undeveloped land. The central and southern areas consist mainly of privately owned housing stock, and there are even some large mansions and properties in this area (including the locally famous Mexican-style ranch mansion on Kurrajong Road owned by the Ingham family, Australia's most famous frozen chicken magnates). Casula Mall, consisting of approximately forty specialty stores, a K-Mart, and Coles and Franklins supermarkets, was opened in 1986.