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.