The profession of nursing has undergone significant changes in Ireland in the last decade, within the wider health service reform context. Determining the optimal nursing skill mix for acute hospitals is perceived as important to ensure the efficient use of the nursing workforce in the provision of safe and high quality care. However, the term nursing skill mix, though widely used, is contested, and practices to determine skill mix in acute hospitals in Ireland are poorly understood. The aim of the study was to examine contemporary policy and practice in determining optimal nursing skill mix in acute hospitals in Ireland. The objectives were to analyse current policy approaches used to determine skill mix nationally and internationally, to examine how the term nursing skill mix is understood and used by managers and policy makers in Ireland and to explore nursing roles in contemporary practice. A review of national and international policy was undertaken highlighting that despite increasing interest nationally and internationally in various approaches to determining optimal nursing skill mix that there is little evidence base for or standardisation of approaches. Following this, semi-structured interviews with 54 nursing managers and policy makers were conducted to explore different perspectives on how nursing skill mix is understood and determined in acute hospitals in Ireland. Themes identified in this study relate to the diversity of influences on skill mix; nursing role ambiguities and inconsistencies in nursing skill mix practices. Results from the quantitative analysis of closed-ended questions confirmed a lack of clarity of who is involved in determining nursing skill mix, the various influential factors and the main principles associated with determining nursing skill mix. The key conclusions of this study relate to the subjective-objective paradox between the complexity of everyday clinical practice settings and the objective methods proposed to determine skill mix and the macro-micro disconnect of methods and approaches across policy makers and nurse managers. There is a need to integrate the macro-micro and subjective-objective tensions in the development of skill mix policy and practice for nursing in Ireland. Adopting effective skill mix practices will facilitate the effective implementation of key healthcare reforms that optimally utilise the nursing workforce.