Australia's fundamental wide area surveillance needs are examined and the characteristics of a surveillance capability are outlined. This is followed by a review of existing and planned area surveillance capabilities. The space environment, remote sensing and spaceborne sensors fundamentals are then summarised to outline the advantages and limitations of conducting surveillance from space. Finally a systems study approach is used to examine the potential of space-based surveillance sensors, including existing and near future technologies, to address the shortfalls in Australia's wide area surveillance capabilities. This systems approach provides a methodology for analysing surveillance system options and gives a readily adaptable framework within which additional research, future system options, changed priorities and new requirements can be incorporated.