Abstract Background: Health workforce supply is critical to ensuring the delivery of essential healthcare, and may be enhanced via mechanisms which alter the scopes of practice of health professions. The aim of this paper is to study the collective perspectives of allied health decision-makers on factors which influence their development and implementation of advanced and extended scope of practice initiatives, and the timing/catalyst and application of their decision-making. Methods: A grounded-theory, qualitative study of the experiences of allied health directors and senior managers across two Australian jurisdictions. Results: Twenty allied health decision-makers met study eligibility criteria. Data coding of interview transcripts identified 14 factors specific to scope of practice change, spanning rational (n=8) and non-rational (n=6) decision-making approaches. Leadership, Governance, Organisational need, Resourcing, Knowledge & Skills – clinical, Supporting resources, Knowledge & skills – change and Sustainability were identified as being rational and enabling in and of themselves, with Leadership seen as being most influential. Comparatively, the non-rational factors of Socio-economic & political environment, Perceived patient need, Organisational environment, Change culture & appetite, Perceived professional territorialism and Actual professional territorialism were more varied, and primarily influenced the timing/catalyst and application of decision-making. Conclusion : Allied health decision-makers hold a complex, systems-level understanding of scope of practice change. Whilst rational decision criteria were predominant and seen to enable scope change, non-rational influences reflected greater variation in decision timing/catalyst and application, thus emphasising the human dimensions of decision-making. Further research is required to better understand how decision-makers integrate and weight decision-making factors to inform the development of structured decision tools.