In respect of professional nursing, the term scope of practice is regularly used, yet is often poorly defined both in Australia and internationally. This study explores the determinants of scope of practice from a national sample of Australian registered nurses using an online survey (Scope-QAu). This paper reports on two parts of a large cross-sectional survey wherein 1231 registered nurses in Australia provided data on how they determined their scope of practice. Scope of practice in the Australian nursing context is influenced by a range of professional publications, guidelines and standards, as well as professional peers and one's own judgement. Findings reveal that few demographic characteristics predicted the way nurses determined their own scope of practice. Nurses commonly relied upon three professional publications, peers and line managers, to establish their individual scope of practice. Impact statement: Registered nurses do not rely solely on professional guidelines or regulatory frameworks when determining their scope of practice.