Another High Court decision on citizenship has triggered four House of Representative's by-elections to be held on 28 July. A fifth by-election for the seat of Perth will be held on the same day following the resignation of Labor MP Tim Hammond. The contests have unimaginatively been dubbed "Super Saturday".

The Turnbull government is now in the last year of its term and in May this year produced its final Budget before the election. The by-elections will provide a crucial measure of support for the government and opposition, and a good performance by the government may tempt the Prime Minister to bring the election forward from early 2019 to later in 2018.

The Liberal Party has announced it will not contest the Labor seats of Perth (ALP 3.3%) and Fremantle (ALP 7.5%), but the other three seats are of enormous interest.

On the northern fringe of greater Brisbane, Labor's hold on Longman (ALP 0.8%) is narrow, and only slightly stronger on the north-west Tasmanian seat of Braddon (ALP 2.2%). Both were surprise Labor gains at the 2016 election, and the loss of either seat would be a blow to Labor Leader Bill Shorten.

To the east and south of Adelaide, Mayo (Centre Alliance 5.0% v Liberal) is a completely different contest. It was won by Rebekha Sharkie in 2016 for the Nick Xenophon Team, the party now re-named the Centre Alliance following Nick Xenophon's resignation from the Senate and defeat contesting March's South Australian election.

Follow the links below for background on each of the seats. ABC News Channel will provide live coverage of the by-elections as results roll in on Saturday 28 July.