Many global cities are rapidly evolving into resource-poor eco-systems, as well as inefficient, unmanageable and unsustainable cities due to population growth and industrialization, which adversely affects economic growth and the quality of life, health and well-being of the communities that inhabit these cities. Furthermore, due to increasing urbanization, such cities struggle with the daily challenges of risks and security issues related to economic, technological and social development, and on the other hand, they also struggle with environmental challenges related to energy, its source and insufficient availability given that conventional energy sources such as fossil fuels are rapidly depleting, while at the same time they are needed to power the physical infrastructure and economy of already overcrowded cities. As a recognized smart city, Barcelona strives to apply technology to create smart solutions for problems that are most relevant to citizens. Furthermore, Barcelona focuses its strategy on the development and implementation of smart technologies while encouraging the initiative of a greener city. The city has additionally leveraged its strategy in a domain that is aligned with sustainability and technology-driven goals related to an eco-friendly environment, affordable housing, urban mobility, waste management, water and energy system development, open data transparency, and a strong digitalization background. Additionally, this paper research how in general all potentially smart cities can be positioned as sustainable and as such follow the example of Barcelona