International audienceThis article, backed by a 2010 urban sustainability qualitative research programme in the Mediterranean, aims at presenting insights on how a crisis context may be the starting point of sustainable urban planning in Tunisia and Spain. It draws some comparisons between Sfax-city three decade-long process of soil pollution clean-up and a formerly prejudiced and excluded neighbourhood of Barcelona known as Trinitat Nova which launched a participatory sustainable urban planning experimentation. Though there was no hypothesis that these two distant examples would a priori share a common starter, these two examples provide comparative grounds for analyzing how urban sustainable solutions may arise from overtly opposed situat...