Brain asymmetry has been observed in vertebrates and invertebrates structurally, functionally, and behaviorally, and can arise through several genetic, epigenetic, or neural mechanisms. It is considered an evolutionary advantage: a functionally asymmetric brain prevents conflicts between both hemispheres, performs a parallel processing of tasks, and avoids duplication of functions, increasing neural capacity. The more lateralized a function, the better it works, although extreme lateralizations are not good: the necessary degree of lateralization depends on the task. This symposium will address structural asymmetries in the human brain, and it will focus on regions involved in language processing, a strongly lateralized cognitive domain. Then, evidence from a behavioral paradigm which measures language lateralization will be presented. This original paradigm has the advantage of being transcultural, and its robust results have been replicated in speakers of different tongues. Finally, the clinical use of this paradigm as a presurgical brain mapping tool measuring language lateralization will be discussed.