Explicit rationing of health care is one of the most important issues under debate in the academic and political fields in both developed and developing countries. The articles presented in this Forum provide an approach to some of the questions relating to this issue. The approach is multidisciplinary, covering complex ethical questions and the contribution of economics to the debate. The analyses reveal specificities associated with the shift from implicit approach for rationing of health care, traditionally dominant in health systems, to a systematic and explicit priority-setting method in general and the potential incompatibility between efficiency and equity objectives in health policy in particular. The Forum's reflections link directly to current worldwide discussions on the questions "Why ration health care?" and "How to ration health care?"