Abstract
Humans continue to face uneven distribution of food, energy and environment protection issues in the 21st century as the second Malthusian trap. In order to overcome these difficulties, we started to think about how to build a new residence in the form of combining economy, environment-friendly and society. Therefore, the concept of 「Eco-city」was risen. After years of development, eco-city, green city, low-carbon island and smart city have gradually been attention in the world. Under the support of community sense and government policy, these eco-cities spring up like mushrooms. Either completed or in progress, eco-cities development are diversified with different backgrounds, cultures and institution. In the study, we choose five cities （ Penhu in Taiwan, Tiangjin eco-city in China, Seoul in Korea, Freiburg in Germany, Samsø in Denmark）and use the methodology of 「Case Study」 to do analysis. We initially classified these case cities into Top-down and Bottom-up, then analyzed the development path, the main analysis unit, to find the hub（government, residents and firms） in the stakeholders network. Second, use the second analysis unit, business model, to analyze investment forms of infrastructure, alternative energy and industry. In the cross-case section, we take 3E（efficiency, efficacy, effectiveness）framework to evaluate these cases, then try to find the differences and key success/ failure factors between them. The result of the study found that it’s important for any eco-city to set target indicators carefully. A good planning should rise life level and boom business activities so that reach better 「social welfare」. Finally, we compared 「Penhu low-carbon island project」currently to other five cases and give some suggestions