This book presents overall communication technologies and protocols used in IoT like in networks: Wi-Fi, Bluetooth, Zigbee, LoRA, GSM/GPRS/EDGE/LTE, etc. in applications: MQTT, CoAP, AMQP, XMPP, etc, focusing on the architecture and threat perseverance of each. The book also presents new/future technological additions like Wi-Fi HaLow (802.11ah), HEW (802.11ax), BLE, NFC, RFID, etc.,) and upcoming changes in communication systems in IoT and its possible security aspects. The book also covers security aspects in communication mechanisms in domain-specific IoT solutions for healthcare, smart cities, smart homes, smart vehicles, etc. The objective of the book is to assist IoT developers to have a good insight into available and upcoming communication technologies so that they can employ the best possible practices while designing and developing IoT solutions.