Health human resources planning is generally based on estimating the effects of demographic change on the supply of and requirements for healthcare services. In this article, we develop and apply an extended analytical framework that incorporates explicitly population health needs, levels of service to respond to health needs, and provider productivity as additional variables in determining the future requirements for the levels and mix of healthcare providers. Because the model derives requirements for providers directly from the requirements for services, it can be applied to a wide range of different provider types and practice structures including the public health workforce. By identifying the separate determinants of provider requirements, the analytical framework avoids the "illusions of necessity" that have generated continuous increases in provider requirements. Moreover, the framework enables policy makers to evaluate the basis of, and justification for, increases in the numbers of provider and increases in education and training programs as a method of increasing supply. A broad range of policy instruments is identified for responding to gaps between estimated future requirements for care and the estimated future capacity of the healthcare workforce.