Humanity is facing an environmental and social crisis that threatens our survival. It has become clear that planning tool able to induce transformative changes is urgently needed. The backcasting methodology could be a good candidate to meet this challenge by enabling planning from a vision. This vision needs however to be defined and described. But definitions of sustainability are numerous, diverse, and none seems to be recognized as the one and only.

With its systematic, rigorous, ethical and sceptical pursuit of truth, sustainability science seems to be an important strategic ally to move towards sustainability. While sustainability definitions have been studied in sustainability science, their contributions to it remained not studied a priori. That is precisely what was studied in this thesis.

I have identified definitions of sustainable states that can strengthen sustainability science in different ways: by contributing to its transdisciplinarity, its consideration for complexity, its participatory potential, and its process orientation. Other contributions have been identified but were not investigated here. Interestingly, no definition capable of contributing in all four ways at the same time has been identified. However, this conclusion needs to be confirmed by further studies, some of which are suggested in this thesis.