The construct of reductionism has taken many forms, but a common feature is that higher level or otherwise complex systems can be understood in terms of (reduced to), the properties of the lower-level elements of which they are comprised. Reductionism as a philosophical doctrine could be considered in an abstract, metaphysical sense, apart from any pragmatic reference. In science, however, it is an important perspective on the relations between domains (physical vs. mental) or levels of organization (e.g., molecular, cellular, tissue, organ, organ system, individual organism, social systems). Consequently, it can impact broadly on issues such as how we approach science and what constitutes a scientific explanation. The issue becomes especially acute for multi-level interdisciplinary approaches in the neurosciences, where the goal is to integrate information across widely disparate levels of organization and function, and associated levels of observation and analysis.