Since the German edition of this book, the topic of risk has experienced even greater attention, not only in the world of science but also in other fields, such as economics and politics. Therefore, many new publications have evolved. To keep with the idea of an encyclopedia for the topic of risk, this book has been completely reworked. Not only are many updated examples included in chapter “Risks and disasters” but also new chapters have been introduced, such as the chapter “Indetermination and risk”. This new chapter was developed since the question “Is it possible for risks to be completely eliminated, and if not why?” has become a major point of concern. Therefore, especially in this chapter, the focus of the book has extended from a simple mathematical or engineering point of view to include much broader concepts. Here, not only aspects of system theory have to be considered, but also some general philosophical questions start to influence the considerations of the topic of risk.