Transvenous implantable cardioverter-defibrillators (ICD) for the primary and secondary prevention of sudden cardiac death due to ventricular tachycardia/fibrillation have led to a significant improvement in survival in high-risk populations. Although conventional transvenous ICD therapy is currently widely used, it is associated with severe intra- and perioperative complications related to the use of transvenous leads, mostly occurring late after implantation. The recent introduction of a new ICD system with fully subcutaneous sensing and shocking capabilities has provided a valuable therapeutic option for special patient groups, allowing to identify and stop malignant ventricular arrhythmias while discriminating them from high-rate supraventricular tachyarrhythmias. This has also given us the opportunity to analyze the advantages and limitations of both implantable lifesaving electrical therapies. In the present paper, the technical characteristics of subcutaneous ICDs are described along with the recent advances in clinical and experimental research that have led to the introduction of these devices into clinical practice (over 1000 patients have been treated worldwide since 2009). Subcutaneous ICDs are indicated for both primary and secondary prevention of cardiac arrest in patients at risk for acquired or congenital arrhythmogenic diseases, including those with an underlying genetic molecular mechanism, provided that they do not require antibradycardia or antitachycardia pacing or cardiac resynchronization therapy, which represent the main limitations of these new devices. A subcutaneous ICD system has the advantage of avoiding the need for transvenous leads, making its implantation or removal much simpler without requiring fluoroscopic guidance. In addition, subcutaneous ICDs can be used in children, young subjects and athletes, and in all patients for whom venous access may be difficult to achieve.