Connections between the left and right brain hemispheres, known as commissures, are essential for coordinating everyday sensory-motor and cognitive functions. Across vertebrates, telencephalic commissures share a similar organization, likely due to highly conserved events of early brain development. However, lineage-specific novelties in commissural systems have also occurred, including axonal rerouting through preexistent tracts, and the origin and expansion of new tracts, such as the corpus callosum. This chapter discusses the phylogenetic history of telencephalic commissures, the possible developmental scenarios involved in the evolution of commissural innovations, and the potential applications of an evolutionary developmental approach to human brain research.