Double dissolutions of the parliament are provided for under section 57 of the Constitution when the House of Representatives and the Senate cannot agree on a Bill. A summary of the steps is set out below:
More than one Bill may provide the basis for a double dissolution. It is possible for a government to save up (or "stockpile") double dissolution bills as 'triggers' during a term of Parliament, in order to get them all passed at the same time.
In exercising the power to dissolve both Houses, the Governor-General acts on government advice.
A double dissolution cannot take place if the term of the House of Representatives will expire within 6 months.
Note that it is only the dissolution which may not occur after this date. The writs must be issued within 10 days of dissolution, and polling day follows between 33 and 58 days after that.
Other issues are the length of the term of Senators following a double dissolution and the time for the next half-Senate election.
There have been six double dissolutions since federation and one joint sitting.
In 1914 and 1983, the government lost the election that followed the dissolution and no further action was taken on the disputed bill or bills.
In 1951 the government won the election with a majority in the Senate and so the deadlock was broken in that way.
In 1974 and 1987 the government won the election but did not have a majority in the Senate. In 1974 the six bills that had been the basis for a double dissolution were passed by the one and only joint sitting. In 1987 the government decided not to proceed with the bill after all.
The double dissolution in 1975 was unusual. According to The Australian Constitution annotated by Cheryl Saunders, more than 20 double dissolution bills had been stockpiled when the Senate 'delayed' three other money bills, including a key appropriation bill. The Governor-General (Sir John Kerr) eventually dismissed the prime minister (Mr Whitlam) and asked the leader of the opposition (Mr Fraser) to take over as Prime Minister on condition that he would advise the Governor-General to dissolve both Houses and call an election (which was held on 13.12.75).
Source: The Australian Constitution Annotated by Cheryl Saunders Constitutional Centenary Foundation 1997 (updated by the AEC)