This compilation thesis identifies and addresses four types of puzzling cases of harm involving individual agents. These types of cases are puzzling due to uncertainty, not regarding the nature of harm, but regarding its normative implications and instantiation under particular circumstances. The relevant types of cases can be divided into two broad categories. In the first category are cases in which we think individuals do harm or act wrongly on account of being involved in harm, but it is not clear what the relationship between the individual act and the harm is, or how the harm makes the act wrong. These cases arise for instance in collective impact situations, where many individual acts together bring about harmful outcomes. In the second category are cases in which it seems that individuals are harmed, but it is not clear whether or how the harm is instantiated. Puzzling cases of the second kind often arise where the alleged harm is tied to the person's coming into or going out of existence, or where birth or death separates the subject of harm from the act or event that supposedly causes it. Papers 1 and 2 each address a puzzling case of harm within the ethics of collective action, while Papers 3 and 4 each address a puzzling case of harm within the philosophy of death and non-existence.