This book provides a comprehensive overview of the rapidly advancing research in quantum networks, both in theory and application. While the classical internet has become essential in our daily lives, its communication techniques have limitations, such as vulnerability to interception and eavesdropping. Quantum networks, by transmitting quantum qubits, address these security concerns using the principles of quantum mechanics, such as superposition, no-cloning, and Heisenberg uncertainty. Kimble first proposed the concept of a quantum internet in 2008, envisioning a network that harnesses quantum devices and laws to transmit information. Wehner and colleagues reviewed the steps necessary to achieve a quantum internet in 2018, outlining development stages leading to increasingly powerful applications. While a fully functional quantum internet is still in progress, significant advances have been made through experiments, such as satellite-based quantum key distribution networks and quantum metropolitan area networks. This book aims to provide a unified theoretical framework for students and researchers interested in the quantum internet, offering insights into topics like network communication theory, secure communication, distributed computation, nonlocality, and quantum configuration. By presenting cutting-edge research and potential applications in the field of quantum information processing, including the quantum internet, this book stands out as a valuable resource for beginners, undergraduate students, graduate students, and researchers in physics, computer science, and information science. It bridges the gap between theoretical perspectives and practical applications, offering a comprehensive guide to the exciting possibilities of quantum networks.