Australia's fertility rate is at an all time low and is well below replacement level. In this article the author summarises some of the arguments that have been put forward to explain what might shape people's hopes, expectations and family decisions. The factors explaining the fall in fertility include broad technological, structural, cultural and social changes, shifting pathways of friends, changes in personal financial circumstances and shifts in the beliefs and values of prospective parents, with one of the most fundamental being postponement of first births and consequent shortened childbearing years, and increased risk of having no children at all. These factors are complex and often mutually reinforcing. The Fertility Decision Making Project has been designed to examine ways in which some of the potential broad social forces may be translated into the decisions individuals make about having children and to enhance understanding of the reasons underlying fertility decisions of men and women.