Australia's party system has long been considered a variation of the Westminster-style two party system ("twopartism" in Sartori's terminology). This is because either the Australian Labor Party (ALP) or the conservative coalition of the Liberal and National Parties has been able to form a single majority government since 1909, when two non-Labor parties fused to form the Liberal Party. At the federal election held on 21 August 2010, however, neither party obtained a majority in the House of Representatives. As a result, the ALP led by Prime Minister Julia Gillard formed a minority government with the backing of 4 crossbench members. This paper analyses whether this election outcome points to the realignment of the Australian party system. Realignment is denned as a significant and durable change in voters' party identification and popular support for the parties. In general, there are three types of realignment: (1) existing major parties adjust their policy position to mirror the new political environment; (2) an emerging party replaces an established major party; or (3) a party system is transformed from one type to the other. The paper argues that the third type of realignment is underway in Australia. The ALP appears to have lost a considerable part of its support base, in particular the so-called metropolitan 'postmaterialist' voters, to the Australian Greens. The Labor Party has also faced considerable organisational problems. Organisational reforms are urgently required but the resistance from entrenched powers remains strong. Electorally and organisationally, the ALP may have lost its ability to form a single majority government. By comparing the Australian Greens' performance in the 2010 election with the Australian Democrats' performance in the 1990 election, this paper argues that the rise of the Greens points to the realignment of the Australian party system and thus the end of twopartism. The evidence is still inconclusive, however, because, according to the 2010 Australian Election Study, only two in five Green voters registered an identification with the party. On a more positive note for the Greens, there has been a significant increase in membership and activities of social movements, especially in environmental and civil liberties issues. For instance, while the national membership of the ALP is now down to 35,000, one of such movements, GetUp!, alone boasts 582,000 members, and the Greens are capitalising on this. If the Greens can take votes and seats away from the Liberal Party as well as from Labor, a realignment of the Australian party system from twopartism to moderate pluralism would be confirmed.