Congenital long QT syndrome (LQTS) is a genetically heterogeneous disorder predisposing to ventricular arrhythmias as well as sudden cardiac death. It has been clearly identified that along with genetically determined mutations, there is a presence or absence of associated genes that can modify the outcome or presentation of the cardiac illness. In this article, we will outline the current knowledge about the genetics of LQTS, its different modes of transmission, role of modifier genes and their combined association with severity.