AIM:To assess the progress and impact of genetic studies in the addictions arena and to present this information in a form accessible to the general readership of Addiction. METHODS:Review of the evidence that genes are involved in addiction, approaches to their identification, current findings and the potential implications. RESULTS:Family, twin and adoption studies provide strong evidence that addiction runs in families and that this is determined in part by genetic factors. Two main molecular genetic approaches, namely linkage and association, have been adopted to identify the specific genes involved. Both methods are fraught with problems. Linkage is limited by issues of sensitivity, and association by false positives. Perhaps the strongest finding in psychiatric genetics to date is the impressive effect that a single genetic variant, in the aldehyde dehydrogenase 2 gene, has on drinking behaviour and reducing the risk of developing alcohol dependence. Other findings are currently less robust; however, the implications of elucidating the genetic underpinning of addiction will be profound. CONCLUSIONS:Addiction genetics is a developing science that has yet to prove its worth in the clinical setting.