This book presents the concepts of the circular economy and sustainable consumption as transformative building blocks for achieving Sustainable Development Goal 12 (SDG 12) of the 2030 Agenda. They are much more than technical changes; instead, they represent a radical reengineering of how societies generate, consume, and reuse resources. The chapter traces the intellectual lineage of these concepts, from The Limits to Growth through Industrial Ecology and Cleaner Production, while positioning circularity as a systemic alternative to linear models that externalize waste and resource depletion. It underscores the critical importance of this shift at a time when climate risks are rising, geopolitical tensions are escalating, and global circularity has regressed to 6.9%, while resource use is projected to double by 2060. This book calls upon readers to move beyond incremental efforts and toward integrated, multipronged strategies that promote economic growth while protecting the natural world. It is intended for students, educators, researchers, and policymakers seeking actionable insights and visionary frameworks to lead the circular transition.