This book offers a new perspective on those El Niños that grow to extraordinary magnitudes, putting forward the claim that these “super El Niños” should be grouped into an isolated cluster. All known super El Niños exhibit pronounced features that are seldom seen in regular El Niños. Super El Niño events, which are marked by a highly deterministic life cycle, will dominate the Earth’s climate for several years. This study identifies the pre-conditions and a booster mechanism that lead to the runaway growth of super El Niños, which is featured by the intense interaction between the anomalous circulation in middle/high latitudes and the ENSO source area. The study not only sheds new light on the fundamental mechanism of the ENSO but also contributes to improving its extended predictability.