My dissertation studies three problems that threaten our functional explanatory practices. The first study, The Normativity Problem and Theories of Biological Function, attempts to explain how it is that biological tokens can perform their functions better or worse, and can retain their functions even when not currently performing them. Etiological theories can try to account for the normativity of functions by cumulative selection or by their contributions to fitness. I argue that neither strategy succeeds. Systemic theories hold that functions are the causal contributions of systemic components to the overall capacities of their containing systems. At first glance, systemic theories do not explain the normativity of functions either. I argue that adding a feedback condition to systemic theories can account for the normativity of functions. The second study, The Malfunction Problem and the Functional Individuation of Biological Traits, attempts to dissolve an apparent paradox about how, if biological traits are functionally individuated, it is possible for an organism to possess a biological trait that malfunctions. The malfunction problem articulates the apparent paradox: A ‘malfunctioning’ trait token seems to no longer belong to its functional type and hence cannot malfunction. I show that distinguishing between the functional type that a token instantiates and the current performance of its function dissolves the paradox. The third study, The Necessitation Problem and the Causal Relevance of Functional Properties, attempts to address a vacuity worry about causal explanation that seems to arise when a property referred to by a causal explanation is individuated by its very effects. Since functional properties are individuated by their functions, and functions are effects, it is hard to see how the ascription of functional properties can play an explanatory role. For the relevant explanations seem to be vacuous: the property that purportedly explains the effect is just the property of having that very effect. I argue that causally relevant functional properties are individuated by historical effects, whereas the effects that they causally explain are current. Since the effects individuating causally relevant properties are distinct from the effects that are causally explained, the vacuity worry does not arise. / Philosophy