About the extent of moral agency in the animal kingdom, one view is that only humans are moral agents. Holding a different view, I argue that moral agency depends on the capacity for other-regard and the capacity to be attuned to significance—such that things matter to one. I derive a criterion where a creature is a moral agent if she performs an action that promotes others’ significant interests and brings great costs to herself where she is aware of these significant interests and imposed costs. Failure to confirm that she has this awareness is a weakness of examples of moral agency in animals that writers provide, since she may be unaware of the significance of what she is doing. Since species of non-ape Primates and aquatic mammals satisfy the evidential criterion, moral agency is likely prevalent throughout much of Mammalia. I consider possible objections from Kant, Singer, and Korsgaard.