RAC3 is a member of the p160 family of steroid receptor coactivators and it is highly expressed in several human cancers, contributing to enhanced cell proliferation and cellular transformation. RAC3 is an underexamined member of the Rho GTPase gene family that is expressed in the developing brain and linked to key cellular functions. The Rac3 polypeptide is highly similar to Rac1, and orthologues of the gene for Rac3 have been found only in vertebrates, indicating the late appearance of this gene during evolution. Rac3 plays an important role in neuronal development and tumor progression, with specificities that distinguish the functions of Rac3 from the established functions of Rac1. De novo missense variants in the homolog RAC1 were recently associated with developmental disorders. RAC3 is a key regulator of adipogenesis since its downregulation generates the cellular arrest and autophagic responses that are required steps for this process.