Mandurah (/ˈmændʒərə/ MAN-jər-ə) is a coastal city in the Australian state of Western Australia, situated approximately 72 kilometres (45 mi) south of the state capital, Perth. It is the state's second most populous city, with a population of 90,306.

Mandurah's central business district is located on the Mandurah Estuary, which is an outlet for the Peel Inlet and Harvey Estuary. The city's name is derived from the Noongar word mandjar, meaning "meeting place" or "trading place". A townsite for Mandurah was laid out in 1831, two years after the establishment of the Swan River Colony, but attracted few residents, and until the post-war boom of the 1950s and 1960s it was little more than a small fishing village. In subsequent years, Mandurah's reputation for boating and fishing attracted many retirees, including to the canal developments in the city's south.

Along with four other local government areas (Boddington, Murray, Serpentine-Jarrahdale, and Waroona), the City of Mandurah is included in the wider Peel region. Mandurah is sometimes grouped together with Perth for statistical purposes, especially since the extension of the Kwinana Freeway and the completion of the Mandurah railway line in the late 2000s. The two cities now form a conurbation along the Indian Ocean coastline, although the Perth metropolitan area officially ends at Singleton around 9 kilometres (5.6 mi) north of Mandurah's city centre.

Mandurah has grown from isolated holiday communities along the shores of the Peel-Harvey Estuary to a major regional city in just over a decade, in a similar vein to the Gold Coast in Eastern Australia. In recent times, it has formed a conurbation with Perth along the coast; it is only 18 km (11 mi) south of Rockingham, a southern suburb of Perth.

Mandurah has also become a popular lifestyle alternative for Perth retirees and its connection with the Perth CBD has been strengthened with the opening of the Perth-Mandurah railway line in December 2007 and a direct road connection to the Kwinana Freeway built by late 2010. A housing affordability survey of 227 cities in 2008 ranked it the least affordable city in Australia.

The waters of the Peel Inlet and Harvey Estuary (one of Australia's larger inlet systems) form the centre of Mandurah. The estuary is approximately twice the size of Sydney Harbour. The city lies in and around this freshwater system which in turn feeds into the Indian Ocean. The city and its suburbs have many kilometres of ocean coastline most of which is sandy beaches. Mandurah also has a number of suburbs built around artificially created canal systems that extend from the Peel Inlet, such as Halls Head, Dudley Park and Wannanup.

In terms of geology, much of Mandurah lies on the dune systems which dominate South Western WA's coastline, progressively grading towards the Swan Coastal Plain as one travels inland. The area has infertile soils due to the dunes being rather sandy, having poor water retention qualities. Limestone outcrops are found to the north of the city especially along the Mandurah railway line. Mandurah is the closest city to Yalgorup National Park which is home to modern thrombolites as well as an array of flora and fauna.

Mandurah is located in the Swan Coastal Plain ecoregion. The ecoregion contains an array of vegetation, from coastal dune and sandplains to banksia and eucalypt woodlands. Mandurah is covered by shoreline and dune deposits from the Pleistocene and Holocene that overlie Paleozoic and Neogene deposits of the Perth Basin. Coastal dunes feature scrub-heath communities, though banksia low woodlands occur on the soils of coastal dunes. Progressing inland give way to eucalypt woodlands.