This book constitutes the refereed post-conference proceedings of the Fourth International Conference on IoT as a Service, IoTaaS 2018, which took place in Xi'an, China, in November 2018. The 50 revised full papers were carefully reviewed and selected from 83 submissions. The technical track present IoT-based services in various applications. In addition, there are three workshops: international workshop on edge computing for 5G/IoT, international workshop on green communications for internet of things, and international workshop on space-based internet of things.