The emergence of quantum computing introduces a significant shift in the digital and security landscape—prompting organizations to reassess the foundations of how we protect information. Systematic Security: Building Quantum Security is a practical guide for security professionals, technologists, engineers, and organizational leaders seeking to prepare for the long-term impact of quantum technology on existing and future systems. In this structured and accessible book, cybersecurity expert Timur Qader presents a step-by-step approach to quantum security. By integrating insights from physics, computer science, and applied cybersecurity, the book explains key principles of quantum mechanics—such as superposition, entanglement, and interference—and examines how these principles can both undermine classical encryption and enable alternative methods for securing data. The book begins by outlining the scientific discoveries that formed the basis of quantum theory, followed by a clear explanation of quantum computing fundamentals. It then guides readers through the current landscape of postquantum cryptography, threat models, and security maturity frameworks. Readers will gain insight into how nation-states, cybercriminals, and enterprises are preparing for the arrival of "Q-Day"—the moment when quantum computers reach the capability to break widely used encryption standards. More importantly, the book provides practical direction on how to prepare. This includes assessing existing cryptographic tools, adopting NIST-aligned transition strategies, and implementing quantum-resilient approaches to identity, detection, cloud infrastructure, and product security. Rather than offering speculation or alarm, this book delivers a grounded and strategic approach to building resilience. It helps readers take concrete steps toward quantum readiness, while also exploring the opportunities quantum technology offers for advancing cybersecurity capabilities. Whether you are maintaining critical systems, developing new technologies, or guiding long term strategy, Building Quantum Security equips you to respond to a rapidly evolving threat landscape shaped by quantum innovation.