Academics, policy-makers and practitioners are increasingly interested in the contribution that effective management of knowledge across organizational and professional boundaries can make to improved public services. Examining knowledge sharing within the context of the UK NHS, we ground our investigation in neo-institutional organizational sociology. We highlight the influence of regulatory, normative and cultural-cognitive aspects of institutions operating in the health care field on the boundaries that impede knowledge sharing. We illustrate how institutional isomorphic processes facilitate convergence within groups of organizations and occupations subject to the same institutional pressures, but, by the same token, inhibit convergence across different organizational and occupational groupings. In short, the development of a learning organization, where knowledge is shared freely across boundaries, will be difficult to realize.