Many countries struggle with the question about sustainability, fairness, and equity of their health systems. With the focus firmly on universal health coverage as a central part to the UN Sustainable Development Goals, there is an opportunity to examine how to achieve optimum access to, and delivery of, health care and services. Underuse and overuse of medical and health services exist side-by-side with poor outcomes for health and wellbeing. This Series of four papers and accompanying comments published in The Lancet examines the extent of overuse and underuse worldwide, highlights the drivers of inappropriate care, and provides a framework to begin to address overuse and underuse together to achieve the right care for health and wellbeing. The authors argue that achieving the right care is both an urgent task and an enormous opportunity.