On the surfacethe two hemispheres of vertebrate brains look almost perfectly symmetricalbut several motorsensoryand cognitive systems show a deeply lateralized organization. Importantlythe two hemispheres are connected by various commissureswhite matter tracts that cross the brain's midline and enable cross-hemispheric communication. Cross-hemispheric communication has been suggested to play an important role in the emergence of lateralized brain functions. Herewe review current advances in understanding cross-hemispheric communication that have been made using modern neuroscientific tools in rodents and other model speciessuch as genetic labelinglarge-scale recordings of neuronal activityspatiotemporally precise perturbationand quantitative behavior analyses. These findings suggest that the emergence of lateralized brain functions cannot be fully explained by largely static factors such as genetic variation and differences in structural brain asymmetries. In additionlearning-dependent asymmetric interactions between the left and right hemispheres shape lateralized brain functions.