Crowds are misleading, both in their simplicity and in their complexity. On the one hand, they behave according to expected trends; on the other, they present sudden shifts and frantic, unexpected behavior. Therefore, "betting against the crowd," whether in politics, sports, or finance, requires a deep understanding of the crowd's dynamics. In this book, Prof. Neuman addresses this challenge by delving into the complexity of crowds. The book involves foundational issues and novel ideas, such as why crowds behave unexpectedly, why betting against the crowd is possible only in short time frames, why is it important to be attentive to suspicious signs that are indicative of the crowd's behavior, and why the long tail of fatalities in armed conflicts leaves us surprised by blitz attacks of violent mobs. The book combines scientific knowledge, experiments, and accessible, often humorous, exposition. It can be read by anyone with a basic science education who seeks to understand crowds and how one can act within and against them.