In this paper, the ontological, terminological, epistemological, and ethical aspects of omission are considered in a coherent and balanced framework, based on the idea that there are omissions which are actions and omissions which are non-actions. In particular, we suggest that the approach to causation which best deals with omission is Mackie's INUS conditional proposal. We argue that omissions are determined partly by the ontological conditional structure of reality, and partly by the interests, beliefs, and values of observers. The final (...) upshot is that moral judgments involved in cases of omissions cannot be grounded on, but are the ground for judgments about what INUS conditions count as omissions. (shrink)