Barley yellow dwarf (BYD) is one of the most widespread and damaging viral diseases of grasses and cereal crops worldwide. Due to an increasing risk of food losses e.g. in barley by Barley yellow dwarf virus (BYDV) as a consequence of climate change, associated by a strong demand to decrease the use of chemical insecticides, breeding for BYDV resistance is of prime importance today. This chapter describes the negative impact of BYDV on barley on multiple levels (anatomy, physiology and agronomic traits). It also demonstrates the benefits of BYDV resistance regarding a reduction in yield losses but also a decreased spread of BYDV in the field due to effects on the tritrophic interaction of virus, vector and plant. Until now, several genes and QTL are known that mediate tolerance or resistance against BYDV, respectively. The combination of genomic tools and phenotyping is the basis for the identification of these genes and recent developments facilitate to enhance this process.