The smart city idea is among the most prominent ones in the world of management. It has also grown in significance for sustainable development among Polish cities. Sustainable development is one of the main goals of modern civilizations, and this chapter examines the concept of a circular economy within that framework. The primary goal of a circular economy is to maximize resource efficiency through cutting down on waste and increasing recycling rates. In this study, we will clarify the scope of projects by outlining six axes that facilitate change in the areas of urban transportation, energy, municipal, housing, health, and the environment. When put into place in a coordinated fashion, these routes lead to green regeneration in urban areas and strengthen their resilience. Through the use of data and technology, “smart cities” aim to improve urban dwellers’ quality of life, economic growth, sustainability, and overall efficiency.