Behavior and welfare are closely dependent on the underlying genetics, yet so far this connection has been poorly investigated. Using domestication as a model, this chapter outlines the fundamentals of genetic inheritance, and explains some central concepts such as linkage, pleiotropy, epistasis, and heritability. It then outlines the essential approaches to finding single genes associated with specific behavioral- and welfare-related traits. These are split into top-down and bottom-up approaches, depending on whether the phenotype or genotype is the starting point for analysis. Finally, the novel field of epigenetics and its importance for welfare science are covered.