Over the past two decades temporary agency work has increased in relation to most sectors and countries. This growth reflects the internationalisation of the agency business which, arguably, has come about due to demands for an ‘on-call just-in-time’ workforce. While temporary agency work possesses several conceptual and empirical challenges for researchers, it also poses challenges for regulators. This paper considers some of those challenges concerning various definitions, classifications and measurement of temporary work while comparing the Australian and Irish experience. It is concluded that while agency work in Australia and Ireland is modest, it is growing, and the conceptual and empirical problems associated with its under-recording pose difficulties for the design and implementation of a regulatory code for this sector.