This book is about the contribution of early warnings to reducing damage, disruption and distress from natural hazards. Its theme is partnership – between producers and receivers of warnings, and between the many experts who contribute to creating a warning. Dedicate this book to everyone who has saved a life by issuing an effective early warning and in the hope that it will be of help to those who we rely on to do so in the future. The background to writing this book is the 10-year High Impact Weather (HIWeather) project of the World Weather Research Programme of the World Meteorological Organization (WMO). The project is, itself, an example of a very successful partnership – across the wide variety of disciplines involved in warning production, between weather services and academia, and between countries.