This article considers the reasons for the development of advanced practice roles among nurses and other healthcare professions. It explores the implications of financial constraints, consumer preferences and the development of new healthcare services on the reorganization of professional boundaries. It makes use of Sir Isaac Newton’s three laws of motion to demonstrate how professional development in nursing has taken place in response to a number of external influences and demands. It also considers the significance of skill mix for the nursing profession, in particular the development and likely expansion of the physician assistant role. The application of different professionals and grades within a healthcare team or organization is central to the Government’s Agenda for Change proposals and nurses have successfully adopted a number of roles traditionally performed by doctors. Nurses have demonstrated that they are capable of providing high quality care and contributing directly to positive patient outcome. Advanced nursing roles should not only reflect the changing nature of healthcare work, they should also be actively engaged in reconstructing healthcare boundaries.