The environmental, socio-political, health and economic crises of recent years are mainstreaming the need to rethink our interaction with the material world. The growing evidence of these crises and their impacts (from droughts to floods, pandemics, wars and the widening gap between the world’s rich and poor) is prompting the gradual development of new paradigm shifts. Among these shifts, we can identify circular economy (CE) and circularity inspired ambitions as a systemic shift aimed at rethinking the world as we know it. CE ambitions are broad and systemic; from questioning the way the biosphere is currently inhabited, to challenging the current systems of production and consumption, and so on. While the CE notion is gaining momentum, it is unfolding excitement and enthusiasm and, at the same time, scepticism and criticism. In this context, our premise is to frame this introductory chapter based on two main questions.Where do circularity inspired ambitions come from? What is the current debate on circularity?A series of complementary sub-questions were also developed to set the scene for the following chapters.How is CE defined and delineated into strategies for implementation? What is the hierarchy of these strategies? When adopting CE strategies, which are the attention points to take into consideration to avoid rebound effects? What are the main future challenges for the development and mainstreaming of CE ambitions and practices? Thus, this chapter introduces the concept of the CE and reveals the potential horizons and obstacles to its implementation in the coming decades. The aim is to develop trajectories of reflection that will set the scene for the other chapters and for future debates. This introductory chapter to the CE is therefore giving an overview of the debate and strategies at a macro level. Based on multi-level socio-technical transitioning pathways (Geels 2005; Geels & Schot 2007), companies are intended as actors of broader business ecosystems (a network of stakeholders influencing ...