Book excerpt: The expression: "We did not see it coming!" has often been heard in recent years from decision makers at the highest levels of responsibility in the private and public sectors. Yet there were actually early (warning) signals, but they were often ignored or not used due to a lack of appropriate methodology. To avoid such blind spots, this book provides answers to the question "how to anticipate". The concept of a "weak signal" is at the heart of the proposed methods. After presenting examples of this concept, the authors provide original and validated answers to questions of feasibility: How to recognize a weak signal? How to exploit it? Numerous applications are presented.