This chapter has mainly presented how to develop a smartphone app. At the beginning, we introduced the development technologies for smartphone apps and the procedure to create a new smartphone app project, so as to give you a general picture of the entire development process. Then, we analysed the functional requirements for each module, namely user management, device provisioning, device control, and scheduling and user centre. At last, we detailed the development process of a smartphone app with source code, and showed how to implement device provisioning and control in the smartphone app.