Plastics, structural polymers made from monomers, are ubiquitous in modern life and have unique benefits. At their end of life, they must be reused or recycled in ways not yet implemented today. In many cases, the polymerization process can be efficiently reversed via depolymerization recycling to regain monomers at the original quality level. As such, depolymerization is a key circularity enabler for some classes of polymers, especially when crosslinked or used in composites. This book introduces the energy, CO2 emission and waste stream dimensions for recycling. It reviews the respective polymer science and introduces the processing technologies for industrial scaling. All these concepts are explored in practical examples across polymer classes and different plastics applications. The economics of depolymerization recycling are introduced, together with life cycle analysis and design for recycling. With this compact overview, a reader will understand depolymerization recycling in the necessary context of scale, sustainability and value chain thinking, towards a sustainable value chain transformation.