Systems of universal health coverage may aspire to provide care based on need and not ability to pay; the complexities of this aspiration call for normative analysis. This special issue arises in the wake of a judicial inquiry into preferential access in the Canadian province of Alberta, the Vertes Commission. I describe this inquiry and set out a taxonomy of forms of differential and preferential access. Papers in this special issue focus on the conceptual specification of health system boundaries and (...) on the normative questions raised by complex models of funding and delivery of care, where patients, providers, and services cross system boundaries. (shrink)