The functions of the Senate are to represent the states equally, and to review and revise the proposals and decisions of the House of Representatives and the executive government.
Equal representation of the states is designed to protect the less-populated states - Western Australia, Tasmania, South Australia and Queensland - against possible domination by the more populous states of Victoria and New South Wales.
Today there are twelve Senators from each of the six states and, since 1975, two from the Northern Territory and two from the Australian Capital Territory, making a total of 76 Senators.
In the case of a double dissolution election - as it is this year (2016) - all Senate seats are available.
This is the only situation where all House of Representatives and all Senate seats are declared vacant at the same time.
And this year, voting rules for the Senate have changed.
This federal election voters will have new ways to decide their preferences on the white Senate ballot paper.
Voters can either number at least six boxes above the line for parties or groups of choice, or number at least 12 boxes below the line for individual candidates.
Senators are elected by a system of proportional representation.
Proportional representation aims to ensure that political parties are represented in numbers that reflect their share of the vote.
The House of Representatives and the Senate have different mechanisms for registering electors' preferences.
Both systems of voting are preferential, in that electors indicate an order of preference among the available candidates.
Preferential voting avoids so-called 'first-past-the-post' systems still in use in many major countries, where the candidate with more votes than any other candidate is elected.
Preferential voting for the House of Representatives is designed to secure the election of one candidate with a majority of votes.
The proportional representation voting used in the Senate is designed to secure the election of several candidates in each state, each of whom obtains a number of votes equal to or exceeding a required quota.
For further information regarding the Senate, please visit
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