As we stand at the dawn of a new computational era, "Quantum Computing: Theory and Applications" is the product of a collaborative endeavor among researchers and educators spanning physics, computer science, engineering, and mathematics. Our collective expertise reflects the multidisciplinary spirit at the heart of quantum computing—a field that challenges the very foundations of information, computation, and technology. The rapid evolution of quantum computing offers not just incremental improvements over classical methods, but a transformative leap promising to reshape fields as diverse as cryptography, artificial intelligence, materials science, and beyond. In this book, we aim to bridge the theoretical underpinnings of quantum mechanics with the practical spectrum of quantum algorithms, architectures, and real-world applications. Each chapter is authored or reviewed by domain experts, ensuring clarity, rigor, and current relevance. We have designed this text for a diverse audience: students embarking on their first journey into the quantum realm, engineers and computer scientists eager to harness new computational paradigms, and physicists seeking interdisciplinary applications of quantum principles. To support varied backgrounds, our style is pedagogical and accessible, providing foundational concepts while integrating advanced topics, illustrative examples, and hands-on exercises. This book is more than a compendium of quantum theory or an overview of applications—it is an invitation to participate in a technological revolution. By demystifying complex ideas and emphasizing both foundational logic and cutting-edge innovation, we hope to inspire readers to join the global effort driving the quantum revolution forward. We extend our heartfelt gratitude to our mentors, collaborators, and students, whose questions and insights have shaped both the content and spirit of this book. May it serve as a guide, an inspiration, and a catalyst for curiosity and excellence in quantum computing.