High use of specialist physicians and specialized procedures coupled with low exposure to primary care are distinguishing traits of the US health care system. Although the tasks of the primary care medical home are well established, consensus on the normative clinical roles of specialist physicians has not been achieved, which makes it unlikely that the specialist workforce is being used most effectively and efficiently. This article describes a typology of specialists' clinical roles that is based on the conceptual basis for health care specialism and empirical evaluations of the specialty referral process. The report concludes with a discussion on the implications of the typology for improving the effectiveness and efficiency of the primary-specialty care interface.