Despite its critical role in restoring cardiac rhythm and thus, in saving human life, cardiac defibrillation remains poorly understood. For a defibrillation shock to be successful, the shock must extinguish existing activation fronts throughout the myocardium without initiating new re-entrant activations. The goal of this paper is to examine the current theories for defibrillation and re-entry induction, the new breakthroughs in the field, and the emerging new hypotheses.