The role of genotyping for diagnosis of the cardiac ion channelopathies is a work in progress. No formal guidelines or other publications discussing current recommendations for genotyping exist, particularly for clinical/commercial genotyping. Further, the field is changing rapidly, opinions vary and, additionally, circumstances inside the US are different from outside. The following considerations are a current summary based on a review of the literature, discussions with experts in the field, and our own opinions and also include a brief discussion about genotyping for therapeutic decision making. Research-based genotyping is very important for continued understanding of the details of pathophysiology and the complex regulatory processes in these diseases. Clinical/commercial genotyping for diagnosis is important for identifying patients with reduced penetrance of the phenotype since effective therapies to prevent sudden death exist. Clinical genotyping for therapeutic advantage has limited application at present but will become much more important if and when genotype-/mutation-type specific therapies are shown to be effective. The recommendations will progressively change as new research findings and new genotyping technologies appear.