This chapter focuses on alcohol dependence (alcoholism), because the diagnosis is more reliable and because most of the genetic data focus on dependence. The earliest genetic association studies in alcoholism were candidate gene studies targeting coding variations in the genes that metabolize alcohol. Certain variations in alcohol dehydrogenases (ADH) and aldehyde dehydrogenases (ALDH) genes have very strong effects on the risk for alcoholism. Variations in other genes appear to have a much smaller effect on risk. Linkage studies and their follow-up, along with candidate gene studies and genome-wide association studies (GWAS), are beginning to fill the gaps. Initial findings must be confirmed in independent studies, and much work remains to elucidate the mechanisms involved. The future will involve studies of epigenetic factors, copy number variants, and gene expression, as well as tests for rare variants of large effect in specific families.