More than half of the world’s population currently lives in cities and this share is to increase to 75?% by 2050. Today the most urbanized regions are Northern America (82?%), Latin America and the Caribbean (80?%), and Europe (73%) (FAO, 2015). The growing population of urban centers and the contributions of urbanization to global environmental change have increased the attention to the sustainability of cities and led to the emergence of the “Green City” concept. How can the “greenness” of a city be assessed? Previous studies have tried to measure cities’ “greenness” through the use of urban indicators, indices, and rankings. They cover categories such as energy, transport, water, waste, air quality, etc. Most of them, though, were conducted only once. Only the European Green Capital award is repeatedly granted since 2010, but doesn’t constantly analyze the same cities. The cities apply voluntarily for the award. The winner city cannot candidate for a period of ten years after receiving the European Green Capital title. The fate of European Green Capitals after the competition is not known. They may flourish or deteriorate.