1The very idea of sustainable urban development implies the undermining of reference frameworks for implementing public policy, individual and collective practices, and of urban engineering. This becomes obvious when considering the issues of adapting to climate change and reducing greenhouse gas emissions to meet the recommended goals established in locally based climate projects. Indeed, their success is related not only with improving energy performance, but also with shaping transportation policies. Research in this area must address alternative modes of transport, and focus on new urban forms and patterns, and on current land uses that sometimes contradict each other or correspond to real or potential changes in way resources are used and distributed.

2For example, in the past ten years, sustainable city policies prioritize climate change concerns at the expense of important issues such as lifestyle or environmental inequalities. Yet, there is no evidence whatsoever that sustainable urban development and the battle against climate change can overlap or even converge. In some cases, requirements contradict. Solutions involve complex trade-offs between factors that are not necessarily the same on both sides of the Atlantic. The contributions presented in this Special Issue of the Urban Environment Journal are drawn from the Journées d’études franco-canadiennes held recently in Grenoble as part of the BABEL series on defining the basic concepts of sustainable development (http://babel.hypotheses.org).