Over the past twenty years advanced nursing roles have become increasingly prevalent in the United Kingdom. A scoping review identified that the traditional scope and boundaries of professional nursing have been reshaped by health service policy and managerial reforms, resulting in advanced nurses focusing less on tasks which were traditionally the domain of nursing, and more on traditionally medical tasks. The research aims were to explore the development and practice of advanced nursing roles in Wales, and analyse ways in which policies and initiatives have influenced the advanced nursing roles. A qualitative approach guided by the principles of Charmaz's (2006) constructivist grounded theory methodology, was used to provide an understanding of advanced nursing roles and the factors influencing them. Semi-structured individual interviews were conducted with forty-five participants: advanced nurses, doctors and managers from two health boards in Wales. All participants had first-hand experience of the advanced roles, and some control over the advanced nursing roles. Documentary analysis was also utilised to contextualise what was said during interviews in order to ascertain the official account of advanced practice and compare this with nurses' reports of current practice. The grounded theory principles of theoretical sampling, coding, constructing categories and developing theoretical concepts, were adopted to produce a theoretical framework explaining the relationships between the emerging categories. The three main categories: working autonomously, reshaping role boundaries and status distinctions, and working relationships, revealed the major paradoxes of advanced practice that emerged from the data. The first paradox concerns advanced nurses' perceptions of their autonomy in making clinical decisions, which was in contrast with their descriptions of direct control by the medical profession and managers, as well as their descriptions of being controlled by protocols and guidelines. The second paradox describes advanced nurses' growing identification with the medical profession as they demarcated boundaries to distinguish advanced practice from other nursing roles, which was in contrast with their desire to be professionally identified as nurses. The third paradox highlights the medicalised task-oriented nature of advanced practice, which prevented many advanced nurses from following patients through and getting to know their patients, versus an idealised view of nursing as delivering personalised, holistic care. The main categories and paradoxes raise questions as to whether advanced nursing roles are advancing nursing, meeting service imperatives, or fulfilling a new doctor's handmaiden role.