The Caucus determines some matters of policy, parliamentary tactics, and disciplinary measures against disobedient parliamentarians.
The leader has historically been a member of the House of Representatives, but though by convention a prime minister is the person who has the support of a majority in the House of Representatives, in the ALP all members (including senators) have an equal vote in the election of the leader, who may then become prime minister.
The word "Caucus" has American roots and was introduced to the ALP by King O'Malley, an American-born Labor member of the first federal Parliament in 1901.
During the leadership contest between Kim Beazley and Mark Latham in December 2003, for example, members of both Left and Right were found in the camps of both candidates.
Factional allegiances in the Caucus tend to be closely related to state political loyalties, and also to trade union affiliations.