J wave syndrome has emerged from a benign electrocardiographic abnormality to a proarrythmic state and a significant cause of Idiopathic ventricular fibrillation (IVF) responsible for sudden cardiac death. Electrical genesis, genetics and ionic mechanisms of J wave syndromes are active areas of research. Typically two of these viz., Early repolarization syndrome (ER) and Brugada syndrome (BrS) are fairly well characterized enabling correct diagnosis in most patients. In early repolarization syndrome,  J waves are seen in inferior (2,3, avF) or lateral leads (V4, V5, V6), while in Brugada syndrome they are best seen in right precordial leads (V1-V3). The first part of repolarization of ventricular myocardium is governed by Ito current i.e., rapid outward potassium current. The proposed mechanism of ventricular fibrillation (VF) and ventricular tachycardia (VT) storms is faster Ito current in the epicardium than in the endocardium resulting in electrical gradient that forms the substrate for phase 2 re-entry. Prevention of Ito current with quinidine supports this mechanism. Morphological features of benign variety of J wave syndrome and malignant/ proarrythmic variety have now been fairly well characterized. J waves are very common in young, athletes and blacks; risk stratification for VF/sudden cardiac death (SCD) is not easy.   Association of both ER syndrome and Brugada syndrome with other disease states like coronary artery disease is being reported frequently. Those with ECG abnormality as the only manifestation are difficult to manage. Certain ECG patterns are more proarrythmic. Individuals resuscitated from VF definitely need an implantable cardiac defibrillator (ICD) but in others there is no consensus regarding therapy. Role of electrophysiology study to provoke ventricular tachycardia or fibrillation is not yet well defined. Radiofrequency ablation of epicardial substrate in right ventricle in Brugada syndrome is reported and is also under critical evaluation. In this review we shall discuss some interesting historical features, epidemiology, electrocardiographic features, and ionic mechanisms on pathogenesis, clinical features, risk stratification and treatment issues in J wave syndromes. Brugada syndrome is not discussed in this review.