A joint meeting of the Australian Parliament is a convening of members of the Senate and House of Representatives sitting together as a single legislative body. Australia has a bicameral federal parliament, consisting of the Senate and the House of Representatives. Subject to the Constitution of Australia, each House has its own rules, standing orders and procedures; its own presiding officer; and meets separately, at dates and times it alone decides. However, there are some occasions when the two Houses have come together as a single body. Reasons for joint meetings The reasons for joint meetings have included: to resolve deadlocks between the Houses following a double dissolution to fill casual vacancies in the representation of the territories in the Senate a special commemorative joint sitting to celebrate the Centenary of Federation secret meetings to discuss security-related issues, such as Australia's participation in war to receive addresses by invited guests such as visiting foreign heads of state or government. Resolving deadlocks between the two Houses The Constitution makes provision for a joint sitting as part of a procedure to resolve legislative deadlocks between the House of Representatives and the Senate. Section 57 provides that, under certain circumstances where there is a deadlock over a bill, both houses may be dissolved in a double dissolution. This is followed by a general election, and the bill may be put to the separate Houses of the newly elected parliament for reconsideration. If this still fails to resolve the deadlock, the bill may be considered by a joint sitting, convened as a single legislative body. If passed by the joint sitting, the bill will be treated for all purposes as if it had been separately passed by the two Houses. The only time such a joint sitting has occurred was on 6–7 August 1974. Casual vacancies in the representation of the Territories in the Senate Between 1980 and 1989 when the Australian Capital Territory (ACT) gained self-government, the choice of a replacement ACT senator to fill a casual vacancy was made by a joint sitting of both Houses. This occurred twice: Margaret Reid was elected on 5 May 1981 to replace the deceased ACT Senator John Knight Bob McMullan was elected on 16 February 1988 to replace former ACT Senator Susan Ryan, who had resigned. Casual vacancies for ACT senators are now filled by the ACT Legislative Assembly, under Section 44 of the Commonwealth