This chapter highlights the genetic resources available for barley, documenting the international genebank collections which house more than 400,000 barley accession including representatives of over 30 wild Hordeum species, cultivated barley (Hordeum vulgare ssp. vulgare) and its ancestral form (H. vulgare ssp. spontaneum). We describe the availability of materials and their information on databases. We also discuss the importance of describing this material in genetic terms. We review the available genetic markers and describe the success of using exotic germplasm to identify new allelic variation for a range of important traits.