Air pollution, environmental degradation, climatic change, resources' depletion are few of the environmental problems that modern society has to face. Also the modern city face problems like the lack of green urban spaces, the increasing use of automobile, the quality of urban life and more. Activists and scientists are trying to find solutions to these problems during the last decades. The ecological city could be one of them, helping simultaneously improve the urban environment and heal the planet. This study attempts to discover the characteristics of this city and present various ways of implementating them in the city. In that thought, the first chapter refers to the social – political context of the ecocity's evolution, while the second presents the characteristics of the ecological city, various indicators of sustainability and application systems. In the third section I present two case studies. The first city I examine is Curitiba, Brasil. A city that was praised internationally for the policies that had followed in the past decades and the first to be called as an ecocity, while the second, Masdar City in Abu Dhaby is a recent attempt to create a city from scratch with zero emissions of carbon dioxide based on renewable energy resources. It would be interesting to see if this concept in the future will be adopted on a bigger scale worldwide or will simply become another trend of urban planning.