This thesis in an invistigation into the concept of "harm" and its moral relevance. A common view is that an analysis of harm should include a counterfactual condition: an act harms a person iff it makes that person worse off. A common objection to the moral relevance of harm, thus understood, is the non-identity problem. -/- This thesis criticises the counterfactual condition, argues for an alternative analysis and that harm plays two important normative roles. -/- The main ground for rejecting the counterfactual condition is that it has unacceptable consequences in cases of overdetermination and pre-emption. Several modifications to the condition are considered but all fail to solve this problem. -/- According to the alternative analysis ...