Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western 33 percent of the land area of Australia, excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to the south, the Northern Territory to the north-east, and South Australia to the south-east. Western Australia is Australia's largest state, with a total land area of 2,527,013 square kilometres (975,685 sq mi). It is the second-largest country subdivision in the world, surpassed only by Russia's Sakha Republic. As of 2021, the state has 2.76 million inhabitants—11 percent of the national total. The vast majority (92 percent) live in the south-west corner; 79 percent of the population lives in the Perth area, leaving the remainder of the state sparsely populated.

The first Europeans to visit Western Australia belonged to the Dutch Dirk Hartog expedition, who visited the Western Australian coast in 1616. The first permanent European colony of Western Australia occurred following the landing by Major Edmund Lockyer on 26 December 1826 of an expedition on behalf of the New South Wales colonial government. Lockyer established a convict-supported military garrison at King George III Sound, at present-day Albany, and on 21 January 1827 he formally took possession for the British Crown of the western part of the continent that was not already claimed by the Crown. This was followed by the establishment of the Swan River Colony in 1829, including the site of the present-day capital, Perth.

York was the first inland settlement in Western Australia. Situated 97 kilometres (60 miles) east of Perth, it was settled on 16 September 1831. Western Australia achieved responsible government in 1890 and federated with the other British colonies in Australia in 1901.

Today, Western Australia's economy mainly relies on mining, oil and gas, services and construction. The state produces 46 percent of Australia's exports. Western Australia is the largest iron ore producer in the world. Its motto is "Cygnis Insignis" ("Bearing the Sign of the Swan"). Its nickname is "The Wildflower State".