A special mechanism under section 57
A double dissolution can dissolve the entire Senate and the House of Representatives at the same time when the conditions in section 57 of the Constitution are satisfied. It is designed around a specific kind of legislative disagreement between the two houses.
That makes it different from an ordinary House dissolution accompanied by a normal Senate election. Political frustration with the Senate is not, by itself, enough to create the constitutional trigger.
The bill must meet the constitutional conditions
Section 57 sets out a sequence involving a bill passed by the House, rejected or not passed by the Senate, or passed with amendments the House will not agree to, followed by a required interval and another relevant passage through the House. The exact legal requirements matter.
More than one bill can potentially provide a trigger, but whether a particular bill satisfies section 57 is a constitutional question, not merely a political label used by the government.
Both houses go to election
In an ordinary federal cycle, only part of the state Senate is normally elected at one time. In a double dissolution, all Senate seats and all House seats are contested. That changes the Senate quota and can alter the electoral dynamics compared with a half-Senate election.
The Constitution also limits when a double dissolution can occur near the end of a House term.
A joint sitting is a later and separate possibility
A double dissolution election does not automatically settle the disputed legislation. If the relevant bill is again passed by the House and again rejected or not passed by the Senate, or subject to unacceptable amendments, section 57 provides a path that can lead to a joint sitting under specified conditions.
Australia has used the joint-sitting mechanism only rarely. It should not be treated as the routine next step after every double dissolution.
How to evaluate a double-dissolution claim
Check the actual bill, the dates and votes in each chamber, the constitutional interval and the text of section 57. Statements that a bill is a 'trigger' are politically significant, but authoritative parliamentary records are needed to understand the procedural history.
The Governor-General performs the formal dissolution on advice within the constitutional framework. Until that occurs, discussion of using a trigger remains political planning rather than a completed constitutional event.
Primary sources and further reading
We use authoritative Australian institutions as the starting point for this explainer. Follow these links for the underlying rules, official guidance and current details.