The Internet of Things (IoT) is the network of physical devices embedded with sensors, actuators, and connectivity which enables these objects to connect and exchange data. Cleary the IoT has a pervasive impact on the society and an increasing number of systems are now based on IoT. One of the key challenges in IoT is coping with the heterogeneous set of systems and the integration of these systems in the same communication network. Several studies have focused on this integration aspect and addressed this at different levels of abstraction. Unfortunately, the different approaches are scattered and fragmented over the different studies and it is not clear how to cope with the integration concern within a single IoT system but also across multiple IoT systems that need to be integrated. To this end this chapter provides a comprehensive and systematic approach for identifying the key integration concerns in the IoT system architecture and describing the currently provided solutions. For this we adopt a pattern-based approach in which generic architecture solution structures are provided to these recurring integration concerns. We illustrate our approach for addressing the integration of IoT based systems within the context of smart city engineering.