In the past 2 decades, advances in genetics have improved our understanding of liver disease and physiology. Firstly, developments in genomic technologies drove the identification of genes responsible for monogenic (Mendelian) liver diseases. Over the last decade, genome-wide association studies allowed for the dissection of the genetic susceptibility to complex liver diseases such as fatty liver disease and drug-induced liver injury, in which environmental co-factors play critical roles. The findings have allowed the identification and elaboration of pathophysiological processes, have indicated the need for reclassification of liver diseases and risk factors and have already pointed to new disease treatments. This is illustrated by the interaction of alcohol, overnutrition and the PNPLA3 gene, which represents an ‘infernal triangle' for the liver. In the future, genetics will allow further stratification of liver diseases and contribute to personalized (precision) medicine, offering novel opportunities for translational research and clinical care of our patients.