This volume addresses the question of the relationship between thought and reality by deploying the notion of sustainability. The key question behind this volume is: What makes thought sustainable? Which is to say: How does the relationship between thought and reality take place and how can it be grounded? Two main answers are given to this question. On the one hand, the nature or structure of reality accounts for the fact that thought is able to truly grasp it; on the other hand, thought has provided itself with the means for grasping reality thanks to its own nature and structure. This volume is explicitly presented as one of several possible paths through the history of philosophy. Many great thinkers are considered, whereas others are not. The Leitfaden keeping together many thinkers from different ages is the very concept of sustainability and how they address the issue of the sustainability of thought. Thus, the volume aims to cast new light on the way some classical thinkers have addressed the issue of the relationship between thought and reality, but also to better understand the concept of sustainability from the point of view of theoretical philosophy.