Genebanks and ex situ collections are essential to conserving maize genetic diversity and enabling global access to those resources. The chapter provides a comprehensive and authoritative review of the key issues facing both in situ and ex situ collections. These issues include better conservation and exploitation of wild varieties and landraces, as well as identifying broader genetic and allelic diversity in Zea and Tripsacum. The chapter includes case studies of the use of exotic germplasm to support breeding of more resilient varieties.