Ensuring AI-enabled Zero Trust Security for Smart City and Healthcare Applications Part A, published as Volume 146 of the serial Advances in Computers, provides a comprehensive examination of the convergence of artificial intelligence, Zero Trust security frameworks, smart city infrastructures, and healthcare technologies. The volume explores how AI-driven security architectures can safeguard increasingly interconnected urban and healthcare ecosystems, addressing challenges associated with IoT networks, autonomous vehicles, wearable devices, telemedicine platforms, medical imaging systems, and healthcare data interoperability. It highlights emerging approaches that integrate AI, blockchain, edge computing, digital twins, federated learning, threat intelligence, and quantum computing to strengthen cyber resilience, privacy protection, and trust management across critical applications. By combining foundational concepts with practical implementations and future-oriented perspectives, this volume serves as an authoritative resource for researchers, cybersecurity professionals, healthcare technologists, and smart city stakeholders seeking to develop secure, adaptive, and resilient digital environments.