Alcohol is widely consumed, but excessive use creates serious physical, psychological and social problems and contributes to many diseases. Alcoholism (alcohol dependence, alcohol use disorders) is a maladaptive pattern of excessive drinking leading to serious problems. Abundant evidence indicates that alcoholism is a complex genetic disease, with variations in a large number of genes affecting risk. Some of these genes have been identified, including two genes of alcohol metabolism, ADH1B and ALDH2, that have the strongest known affects on risk for alcoholism. Studies are revealing other genes in which variants impact risk for alcoholism or related traits, including GABRA2, CHRM2, KCNJ6, and AUTS2. As larger samples are assembled and more variants analyzed, a much fuller picture of the many genes and pathways that impact risk will be discovered.