Most red team efforts fail not because they are technically weak, but because they cannot survive the realities of enterprise environments. Building a Red Team moves beyond tools, exploits, and one-off engagements to focus on what actually makes adversary simulation effective at scale: sound design, disciplined operations, stakeholder alignment, and clear communication of impact. Written by leaders who have built and run red teams inside large, complex organizations, the book explains how to create a red team program that delivers sustained security improvement rather than fleeting 'gotcha' moments. Instead of teaching readers how to break in, the authors focus on how to make red teaming matter. Readers learn how to define purpose and scope, plan meaningful operations, partner productively with defenders and leadership, manage safety and risk, and translate uncomfortable findings into action. The emphasis is on judgment, structure, and repeatable frameworks-so teams understand why they do what they do, not just how. The result is a practical, experience-driven guide for anyone responsible for turning red teaming into a credible, trusted enterprise capability.