This chapter will primarily focus on the early repolarization (ER) syndrome that is known to increase the risk of sudden cardiac death and is of particular concern to the electrophysiologist. ER pattern is quite prevalent and is commonly seen in young, healthy individuals who are likely at low risk of sudden cardiac death. The distinction between ER syndrome and the ER pattern on ECG is the key. ER syndrome can be diagnosed only in patients resuscitated from otherwise unexplained ventricular fibrillation (VF) or polymorphic ventricular tachycardia (VT) who meet criteria for the ER pattern on electrocardiogram (ECG). This chapter also discusses the epidemiology of ER, molecular mechanisms of the J-wave, ST elevation, and VF, association to ventricular arrhythmias and sudden death, and risk stratification of sudden death. Current HRS/EHRA/APHRS expert consensus recommendations on therapy for ER syndrome are also outlined in this chapter.