This paper seeks to generate an understanding of the decision-making process of Australia's largest union, the AMWSU. It is divided into five sections. Section I contains a description of the union, with particular attention to historical influences on its current behaviour. Section II details the author's research program and methodology. The author's findings are presented in Section III in a framework illustrating “what” decisions are made, “how” they are made, and “who” is involved. Section IV draws some tentative conclusions about decision-making in the union. Finally, Section V identifies some recent developments which affect the degree of democracy in the AMWSU.