Recent years have seen a substantial increase in the amount of research concerning sex/gender differences in the human brain. In this chapter, we review and synthesize some key research findings concerning sex/gender differences in brain structure, brain function, and structural/functional connectivity. In light of the findings, we concluded that although sex/gender differences in the brain exist at multiple levels, results in some areas are inconsistent, partly because the large inter- and intra-individual variability within each sex/gender has not been sufficiently considered. Consequently, neuroscience research should routinely include both men and women. Moreover, concepts referring to “male brain”, “female brain” or “sexual dimorphism” are outdate and incorrect, and therefore should be avoided in the neuroscientific literature. Finally, neuroscientists with a focus on sex/gender difference should adopt a psychobiosocial approach whenever possible, because structural and functional differences in the brains of men and women will never be fully understood, if psychological, biological and environmental/social factors are not routinely taken into account in combination.