Abstract
The growing flow of people into cities causes several challenges for their functioning. This brings the need to ensure, for example, efficient transport, sustainable waste, and appropriate energy policy. Particularly capital cities are exposed to the above-mentioned risks, due to their large numbers and densities of inhabitants. Therefore, the state of the environment in cities should be monitored systematically. The research aim of this article is to evaluate the level of environmental sustainability in capitals of European Union countries. A synthetic indicator was made up of diagnostic variables, using quantitative and qualitative indicators relating to the quality of the environment. Based on the ranking, results reveal that Europe is spatially divided according to the level of environmental quality. The best results were achieved by capital cities of the northern European countries. The analysis presented here has some application potential. It can serve to identify challenges to improving the quality of the environment, and to raise public awareness of the importance of changing individual behaviour (e.g., use of public transport).