Building the virtual replicas that will reshape industry, security, and science Everyone is investing in AI. Few are engineering it. This book introduces AI-powered digital twins and shows how to build them. AI Powered Digital Twins lays out a 12-layer engineering architecture -- from raw data ingestion through semantic spine, event-native core, asset tagging, agent reasoning loops, simulation, Zero Trust security, and governance lifecycle -- designed for systems that must perform in the real world. Hala Nelson came to AI through mathematics and the demands of real-world systems. She brings that rigor and practicality to the central problem the field is avoiding: AI-powered systems need a standard of care, the same way bridges, aircraft, and operating rooms do. The book explains how to construct a digital twin that stands up in the real world -- agents that reason, act, and stay governed; an AI and data strategy that translates directly into measurable business value rather than a policy document that sits on a shelf; accountability frameworks that hold AI systems to the same standard as aviation, healthcare, and civil engineering; and the engineering discipline to sustain it all as a living system. 17 chapters. One architecture. Zero hand-waving about security. This is an essential read for engineers, architects, technical leaders, business strategists, and the policymakers who operate in this world.