Modern cities are deploying smart, safe, and sustainable smart city services. However, such services are largely fragmented across cities because they are being developed based on proprietary IoT solutions or using different IoT standards. This creates a strong need to develop an approach to bridge disconnected smart cities and provide interoperability. Therefore, the aim of this article is to provide a guideline to mayors and other city officials for interconnecting their smart cities with other smart cities for interoperability. For this purpose, we propose three interworking models that can be selected based on the status of the cities to be connected with each other. All these models enable the continuity of IoT services between cities using different technologies, that is, a standardized interface, interworking proxy, and semantics. As only one model cannot be adapted to all the connected city cases, we thoroughly compare and analyze the models followed by introducing the pros and cons of each model.