Abstract
This article examines massive multiple realization (MMR) in the context of neurobiology. It highlights the differences in the conception of multiple realization and its methodological implications by researchers in the philosophy of psychology and those in the philosophy of neuroscience. It discusses neurobiological findings about MMR and shows that there is plausibly important individual variation at every physiologically significant level of organization in the nervous system. It explores philosophical concerns about the MMR hypothesis and proposes a framework for realization and multiple realization.