Lignocellulosic biomass comes from different sources: waste from industry or agriculture or dedicated production. The plant species used for this dedicated production must primarily meet the expectations of high yields and can also have varied compositions which can be more or less suitable to certain uses. Furthermore, in addition to variations in the quantity and quality of biomass produced between species, there are variations of composition and yield between different genotypes within each species. Thus, beyond the impacts of environmental factors, genetics is one of the factors which acts on the variation in yield and composition of lignocellulosic biomass within a species. This opens the way to the selection of genotypes suitable for industrial processes without losing their agronomic abilities. This chapter illustrates both the genetic and genomic approaches and the results obtained in different species used for the production of lignocellulosic biomass, such as salicaceae (poplar, willow) and C4 grasses (maize, sorghum, Miscanthus).