The concept of sustainable cities is based on a development paradigm that recognizes the rapid growth of urban population and makes an important contribution by forming a global urban plan. Sustainable city is organized in order to emphasize the importance of people and their needs. This paper will define what sustainable city is and show how certain innovative elements have been introduced in Copenhagen in order to achieve city sustainability. In that regard, an overview of innovative urban solutions in the context of environmental protection will be given. A comparative analysis of the achievement of the SDG 11 objective - Sustainable Cities and Sustainable Communities in Copenhagen will be carried out in relation to the other European Union capitals. The aim of this research is to determine whether Copenhagen is a sustainable city and how sustainable cities contribute to promoting the sustainable development goals. Finally, proposals will be made to achieve those objectives for other cities, based on the results achieved by the City of Copenhagen.