Thinking about sustainable actions for big cities is one of the problems of the twenty-first century. This demand is faced by cities in the different dimensions that make it up: social, economic, and environmental. Just as companies should think about adopting and investing in Environmental, Social, and Governance (ESG), cities need to become smart cities, an important step to transform themselves into sustainable cities with a higher quality of life. ESG, in companies, refers to the three central factors for measuring the sustainability and social impact of an investment process. Cities need to focus, in addition to modernizing their infrastructure, on strengthening the circular economy, investing more in education, reducing school dropout, which is closely linked to the area of security in cities, and based on these measures, seek balance in all areas of society. The concepts of smart cities and sustainable cities will be presented, showing the interconnection of both concepts. The purpose of this chapter is to show how to build smart cities and how they are transformed into sustainable cities. Thus, a systematic and integrative review was carried out in the Scopus database, in order to answer the following questions: (1) What are smart cities? (2) How to transform cities into smart cities? (3) What is the interconnection between the two concepts: smart cities and sustainable cities? (4) How do smart cities contribute to building a sustainable city? The results converge in the relationship between intelligence and sustainability, being the basis for a new type of city that directs its growth in an intentional, collaborative, and inclusive way to transform urban centers into a place with a higher quality of life. This chapter brings two examples of smart cities: one in Portugal and another in Brazil, explaining how the national legislation of each country and its social reality interfere in the construction of smart cities. The main innovation presented is the indicators for transforming smart cities into sustainable cities. For this purpose, the chapter is divided into eight sections, which are entitled: Introduction, Smart Cities, Sustainable Cities, Methodology, Relationship Between Sustainable Cities and Intelligent Cities, From Smart Cities Toward Sustainable Cities: Inclusion and Life Quality, Case Studies: Smart Cities from Brazil and Portugal, and Conclusions.