 Trends during the first decade of the twenty-first century in philosophy of neuroscience included renewed interest in the nature of mechanistic explanations. This was in keeping with a general trend in philosophy of science (e.g., Machamer, Darden, and Craver 2000). The application of this general approach to neuroscience isn’t surprising. “Mechanism” is a widely-used term among neuroscientists. In his book, Explaining the Brain (2007), Carl Craver contended that mechanistic explanations in neuroscience are causal explanations, and typically multi-level. For example, the explanation of the neuronal action potential involves the action potential itself, the cell in which it occurs, electro-chemical gradients, and the proteins through which ions flow across the membrane. Thus we have a composite entity (a cell) causally interacting with neurotransmitters at its receptors. Parts of the cell engage in various activities, e.g., the opening and closing of ligand-gated and voltage-gated ion channels, to produce a pattern of changes, the depolarizing current constituting the action potential. A mechanistic explanation of the action potential thus countenances entities at the cellular, molecular, and atomic levels, all of which are causally relevant to producing the action potential. This causal relevance can be confirmed by altering any one of these variables, e.g., the density of ion channels in the cell membrane, to generate alterations in the action potential; and by verifying the consistency of the purported invariance between the variables. For challenges to Craver’s account of mechanistic explanation in neuroscience, specifically concerning the action potential, see Weber 2008, and Bogen 2005.