The Internet-of-Things (IoT) is a revolutionary technology that is rapidly changing the world. IoT systems strive to provide automated solutions for almost every life aspect; traditional devices are becoming connected, ubiquitous, pervasive, wireless, context-aware, smart, controlled through mobile solutions, to name but a few. IoT devices can now be found in our apartments, places of work, cars, buildings, and in almost every aspect of life. In this investigation, we propose an IoT system Development Model (IDM). The proposed IDM enables the development of IoT systems from concept to prototyping. The model comprises concept refinement pyramids, decision trees, realistic constraint lists, architecture and organization diagrams, communication interface patterns, use cases, and menus of analysis metrics and evaluation indicators. The investigation confirms that the proposed model enjoys several properties, such as, clarity, conciseness, thoroughness, productivity, etc. The model is deployed for a variety of systems that belong to heterogeneous areas of application; the model is proven to be effective in application and successful in integrating mobile solutions. This chapter includes the presentation of the IDM sub-models, the reasoning about their usefulness, and the technical developments of several systems. The chapter includes thorough discussions, analysis of the model usability and application, and in-depth evaluations. 23 rely on services hosted by a third-party Internet provider. Here, the interfacing device and the user fully communicate through the third-party provider, such as, a webserver, database server, application server, etc. RECON adopts the second CI model that comprise a server-based interface with a dedicated Internet Protocol (IP) address. All the presented systems benefit from the third model that enables a direct communication between the user and the processing system when the user and the device are at the same location. Indeed, in all the presented applications, the user communicates with the system using a mobile solution that can be an application or a web-interface using a browser. Figures 14 and 15 show snapshots of the mobile user interfaces of RECON and NFC Wallet.