Difficulties in medical ethics are traditionally discussed in relation to problem arising in clinical care between individuals: disagreements between patients and health care providers as to the best course of action, confidentiality, end-of-life choices, how to make ethically justifiable decisions for patients who are incapable of decision-making, and the like. Difficulties related to fairness, to sharing what resources we have equitably in caring for the sick, pose a special challenge. They are situations where thinking in terms of individuals tends to be less helpful. To address these issues, we need to think in terms of groups. In terms of weighing conflicting claims in a way that can be justified as fair overall, as well as to the individuals involved. This thesis explores the practice of clinical rationing, and the ethical issues associated with it, with a particular focus on fairness. We conducted studies showing that doctors ration care and realize that they do so, that they attempt to include various concerns for fairness in their allocation decisions, and use various strategies for doing so. Some of these strategies are exactly the sort which we would expect to target known inequalities within health care. All these results should at least partly reassure us as to the acceptability of clinical rationing. However, there remains considerable room for improvement, both in our knowledge and practice of clinical fairness. Limit-setting decisions made within clinical practice by doctors have been critiqued as ‘implicit rationing', in part because of their hidden and unexamined nature. In this thesis, and through the various studies described here, my colleagues and I have attempted to throw some light on the difficult, less articulated, sometimes surprisingly complex, and always necessary processes through which resource allocation decisions are made in day-to-day clinical practice. Opening this field to discussion is important. As shown in one of the studies presented here, we have in Switzerland a health care system under pressure. Doctors report feeling threatened, and also report that they set limits: almost as though this were a form of defensive medicine. They further report unequal success in defending justice-based values, although they consider them important to their practice. In such a context, articulating what fairness in clinical care means, and why it is important, takes on a special kind of urgency. Therein may be a hope of opening a necessary debate on what we consider to be reasonable and fair ways of setting limits in the health care which will be available to us.