IoT Architectures and Protocols is a comprehensive academic resource that explores the technological backbone of the Internet of Things (IoT). Authored by a team of experienced educators and researchers-Dr. M. Lily Florence, Mr. P. Ashok Kumar, Dr. Shaik Fairooz, and Mr. N. Srikanth Prasad this book offers a deep dive into the multifaceted world of IoT systems, architectures, and communication protocols. It is published by Quill Tech Publications and is intended for students, educators, engineers, and professionals interested in building expertise in IoT infrastructure and development. The book begins by introducing the evolution of IoT, outlining its definitions from various industrial, academic, and consumer perspectives. It elaborates on the key components of IoT ecosystems sensors, actuators, connectivity technologies, and cloud platforms while examining the layered technology stack that supports real-world IoT deployments. The text progresses through core IoT concepts such as data collection, processing, and transmission, supported by enabling technologies like AI/ML, blockchain, and edge computing. A dedicated section compares IoT with Machine-to-Machine (M2M) communication, clarifying architectural and functional distinctions while highlighting the convergence of both technologies. The book then delves into network protocols across all layers from data link and network layers to transport, session, and application layers covering standards such as Zigbee, BLE, CoAP, MQTT, HTTP, and many more. Further chapters address service-layer protocols, security frameworks, and virtualization technologies like Software-Defined Networking (SDN) and Network Function Virtualization (NFV), showcasing their role in enhancing scalability, flexibility, and security in IoT environments. Real-world case studies and use cases from smart cities, healthcare, agriculture, and manufacturing bring technical concepts to life, emphasizing practical relevance.