There is an increasing interest in assessing unmet need for health care services particularly in European countries. Despite this there has been relatively little analysis of unmet need in the European or wider international setting. It remains a challenge to pin down what types of unmet need can and should be addressed by health care policymakers, and how to go about identifying and quantifying those unmet needs. The objective of this paper is to propose a new way of thinking about unmet need for health care which can in turn guide analysis of unmet need in terms of potential data sources and analytic approaches. Unmet need is shown to be a complex multi-faceted concept that cannot be captured by a single indicator or measurement. To advance the literature in this field, this paper considers what happens to unmet need over time. By introducing a dynamic perspective, three alternative trajectories for health care needs are outlined: non-use of health care, delayed use of health care and sub-optimal use of health care. These trajectories are discussed with a view to improving the focus, and policy applicability, of empirical research in this field.