 ‘Functional reduction’ signifies a family of models which are concerned with the reduction of such causal, computational, or goal-related properties. These models describe reduction as consisting of a relation between a functional property P and a structural or substrate property P* that plays the role determined by the functional property P, or at least does in a restricted class of systems or contexts. This general description leaves the question of the exact relation between P and P* open, nor does it say anything about the specific epistemic status of functional reduction. On this issue different models of functional reduction disagree.