Implantable cardioverter-defibrillators (ICDs) detect ventricular arrhythmias responsible for causing sudden cardiac arrest and then deliver a high-voltage defibrillation shock to terminate the arrhythmia and restore normal cardiac function. Conventional transveneous ICD (TV-ICD) systems require one or more leads to be implanted into the heart through the venous anatomy. While TV-ICDs are well tolerated by most patients, the invasive approach can be associated with severe complications, including systemic infection, cardiac injuries, and lead failures. An entirely subcutaneous ICD (S-ICD) system was developed as a less invasive alternative to TV-ICDs without requiring leads in or on the heart. The S-ICD system provides therapy with a left lateral pulse generator and parasternal electrode configuration that is placed under the skin outside the rib cage, resulting in a much lower risk profile. Advances in defibrillation research and far-field sensing combined to enable development of the commercial S-ICD system. An investigation device exemption (IDE) clinical investigation followed, with FDA approval in September 2012. Evaluation of the long-term performance of the S-ICD system continues, with two independent postmarket registries and a prospective randomized head-to-head trial versus the transvenous ICD.