The current chapter reviews our progress in understanding how genes influence eating disorders by addressing the following areas: (1) how recognition of genetic influences on eating disorders emerged; (2) the complexities of gene environment interplay; (3) what twin studies can tell us about gene environment interplay, and (4) the current state of molecular genetic studies. It is concluded that both genes and nonshared environment play a critical role in the explanatory framework for the etiology of eating disorders. Shared environment is likely to contribute to the development of cognition and attitudes that may initiate disordered eating practices. Researchers are on the cusp of identifying specific genes that are implicated, and explication of the manner in which genes and the environment work together to increase risk for eating disorders hinges on the collection of larger samples.