Urban areas are increasingly recognized as strategic sites to address climate change and environmental issues. Specific urban projects are marketed as innovative solutions and best-practice examples, and so-called green cities, eco-cities and sustainable cities have emerged worldwide as leading paradigms in urban planning and policy discourse. The transformation of cities into eco-cities (Kenworthy, 2006;Roseland, 1997) is often based on big data and -widely varying -indicators that should proof the success of urban climate governance (Bulkeley, 2010). The European Commission with its 'Green Capital' program, Britain's 'Sustainable City Index', France's 'EcoCite´' scheme, the US-American's 'Greenest City' ranking developed by WalletHub's, the US and Canada 'Green City Index' sponsored by Siemens -these programs are all examples of public and private initiatives aimed at identifying and ranking the 'greenest' city or cities according to a competitive rationality. They are mostly quantitative approaches, based on 'hard' and 'scientific' indicators that allow cities to be compared according to their efforts in sustainable urban development. Using these indicators, cities worldwide have increasingly promoted sustainability initiatives in order to position themselves advantageously on the global scene (Chang and Sheppard, 2013;Cugurullo, 2013;Swyngedouw and Kaika, 2014;While et al., 2004).These urban ranking efforts tie into the fact that sustainability has become a metaconsensual policy term (Gill et al., 2012), resting upon broad support from diverse sectors of society. Promoted at first as a way of bringing forward an ecological urban agenda connected to social development, sustainability has lost much of its transformative potential. By now, even car manufacturing in Germany, oil pipelines in Alberta, Canada and nuclear power plants worldwide are being politically justified with reference to sustainability and climate change prevention. Despite controversial national positions regarding the processes, pace and extend of implementing environmental policies -a divergence that became very evident, for example, during the 2009 United Nations

An enigma lies at the heart of this article. In December 2006, the mayor of Saint‐Étienne, Michel Thiollière, was elected as the fifth best mayor in the world by the internet site City Mayors. Yet no publicity was made locally around this award. Taking this anecdote as a starting point, this article deals with the motivations that can lead a city mayor to become involved in urban international relationships' policy (city twinning, participation in cities networks, study trips, etc.). On the one hand these activities provide resources for building up political legitimacy and for electoral control, and on the other they provide resources for policy solutions to urban problems in the public realm. Nevertheless, in a context of transformation of the process of legitimization of urban elected officials, the second kind of resources seems to be the most sought after in mayoral involvement in international activities.