This document specifies an Internet of Things (IoT) reference architecture (IoTRA). The IoTRA is a generalization of existing practice including the distinguishing characteristics of IoT systems and other fundamental characteristics exhibited by IoT systems. The IoTRA addresses stakeholder concerns related to the business value of IoT systems. The IoTRA also addresses the interactions between the IoT system, the users, and the physical environment. Implementation of IoT systems is also addressed in this document. Among the characteristics specified in the IoTRA are abstract functions within IoT systems and a variety of structures that are used to construct IoT systems.