This essay presents a brief review and evaluation of some guiding concepts during the past century of inquiry into localization of brain functions. Mapping methods are described and discussed as one useful set of approaches to defining functional localization. Each neurobiological discipline: neuroanatomy, neurophysiology, neurochemistry neuropsychology, neuroethology, clinical neurology, biophysics and bioengineering, all use map-making strategies in their search for valid spatial and temporal definitions of the phenomena in their field of interest. Particular emphasis is given to neurophysiological mapping procedures. How these procedures have evolved to become important tools for testing hypotheses about the neuroelectric, behavioral and psychological functions of specific neuroanatomical structures is discussed. The continued importance is emphasized of neurophysiological mapping as a basic set of descriptive sampling strategies for testing hypotheses about specific neural mechanisms and their adaptive operations.