This book constitutes the thoroughly refereed proceedings of the 3rd International Conference on IoT as a service, IoTaaS 2017, held in Taichung, Taiwan, in September 2017. The 46 full papers were carefully selected from 65 submissions. The papers deal with the "Everything as a Service" deployment paradigm which enables the easy adoption of IoT based services and applications by end-users, and forces providers of smart objects and middleware platforms to architect their solutions accordingly. The three special sessions organized were Wearable Technology and Applications (WTAA), Building Smart Machine Applications (BSMA), and Security and Privacy in Internet of Things, Services and People (SP-IoTSP). The WTAA special session aimed to address the challenges of maintaining high efficiency of WTAA in terms of high recognition rate, energy consumption, computational costs and so forth. The BSMA special session aimed to explore how to construct smart machines architecture for the industry under the background of IoT and big data. The SP-IoTSP special session aimed to investigate recent research and future directions for IoTSP security and privacy.