This book presents a systematic and comprehensive overview for IoT security. It first introduces architecture approaches for IoT and IoT security, describing the security techniques for different layers in the IoT security architecture. It also provides an in-depth analysis on the difference between IoT security and traditional system and data security. It is commonly known that information security includes data confidentiality, data integrity, and availability, and that measures include non-repudiation and access control. However, in practical IoT system construction, many more security measures need to be carefully considered. As such, this book presents around 60 different security measures, mainly focusing on the sensor layer of IoT. These security measures can serve as a source of reference for IoT system construction, as well as IoT security standard making.