In this chapter we examine the ingredients of culpable omissions. We first look at the various triggers of duties to act. Some of those duties are triggered voluntarily, as when one marries or contracts. But others are created by acts that place others in peril, a potentially quite capacious category of acts, as we illustrate. We then assume a duty to act and ask what has to be the case for the failure to act to be culpable. We conclude that the actor must be aware of the facts that trigger the duty, aware that the victim is at risk of harm, aware of the actor’s ability to avert that harm, aware of the level of risk occasioned by acting to avert the harm, and unaware of facts that would justify omitting to act. Finally, we consider how to calculate the overall culpability of one whose failure to act is culpable at different levels over its duration.