This chapter focuses on the genetic factors influencing the development of eating disorders (EDs). One strategy for identifying the genetic influence on EDs has been to determine whether particular psychiatric disorders or traits are expressions of a shared genetic diathesis. Two genetic strategies have predominantly been used to identify susceptibility loci for EDs on the human genome: linkage-type analyses and association studies. Linkage studies test the hypothesis of co-segregation between a marker locus and a trait within families. Association studies test whether an allele and a phenotypic trait show correlated occurrence within a population. The available data strongly suggest that the genetic influences reside in multiple genes and reflect interaction between multiple genes and the environment. The identification and analysis of endophenotypes related to EDs can therefore be of great importance for determining the genetic mechanism underlying EDs.