Germplasm banks, such as CIMMYT’s, have been the ex situ sources of crop genetic diversity for plant breeders and researchers for decades. Increasingly, these institutions are providing seed from ex situ collections and technological support directly to smallholder farmers, who have always been the in situ guardians of landraces. In the case of maize in its center of origin, mounting evidence suggests that accelerating loss of genetic diversity may indeed impact the ability of this critically important crop species to adapt to the changing environments of the future.