This chapter introduces the six key factors described so far as infrastructure for the digital society and the tools necessary to utilize them toward creating a people-centric sustainable smart city. In order for a wide variety of players participating in smart cities to collaborate under a common goal, one of the challenges is to have a common understanding of how far each city and area has been formed and what the next goal is. Besides, there is no common rubric that clearly articulates the expectations for each developmental step or level toward achieving a people-centric city. This chapter discusses in the following structure. Section 14.1 summarizes such challenges to consensus building and phased development. Section 14.2 defines the steps to incrementally implement six key factors in cities and regions. Here a common four-step template is given, which is then applied to six key factors, i.e., Social Acceptance, Data Governance, Citizen Participation, QoL-based Assessment, Human Resource Development, and Data Ecosystem. Section 14.3 discusses the phased implementation of smart cities using these concepts, and finally Sect. 14.4 summarizes the key factors as infrastructure in a digital society.