The fascination of seasonal climate forecasting, for which El Niño forecasting provides the prime basis, derives from its multi-faceted character. Not only does it pose exciting new scientific challenges for the climate community, but it is linked naturally to a great variety of key practical concerns, from security related issues, such as water resource management, food security, and disaster prediction and prevention, to health planning, agriculture management, energy supply, and tourism, to name but a few. Seasonal to interannual climate forecasts are indeed becoming a most important element in certain policy/decision making systems, not least within the contexts of sustainable development and of climate change adaptation.