Shared care across the primary-specialty interface has been defined as the joint participation of primary care physicians and specialty care physicians in the planned delivery of care, informed by an enhanced information exchange, over and above routine discharge and referral notices. As such it has the potential to improve the management of chronic diseases and lead to better outcomes than either primary or specialty care on their own. This review examines the effectiveness of shared care for a range of chronic conditions in a variety of healthcare settings. Shared care interventions identified were complex and multifaceted. Results were varied and many of the studies were of poor quality. Shared care had a clear effect on improving prescribing but the pattern of results was mixed for all other outcomes. There is a need to improve the design and quality of studies examining such interventions in order to determine which components, if any, are effective, to assess issues such as sustainability of shared care and to determine settings and patient groups in which shared care may be most effective.