This paper examines the standard view of realization operative in contemporary philosophy of mind, and proposes an alternative, general perspective on realization. The standard view can be expressed, in summary form, as the conjunction of two theses, the sufficiency thesis and the constitutivity thesis. Physicalists of both reductionist and anti-reductionist persuasions share a conception of realization whereby realizations are determinative of the properties they realize and physically constitutive of the individuals with those properties. Central to the alternative view that I explore here is the idea that the requisite, metaphysically robust notion of realization is ineliminably context-sensitive. I shall argue that the sufficiency and constitutivity theses are typically not jointly satisfied by any one candidate realizer, and that going context-sensitive in one's metaphysics is preferable to the standard view. The context-sensitive views developed here are implicit in a range of common views in both the philosophy of mind and the philosophy of biology, even if they have not been explicitly articulated, and even though they undermine other views that are commonly endorsed.