This chapter introduces the product life cycle, covering phases from development and production to use, maintenance, and end-of-life. Parallel technology cycles trace innovations from introduction to maturity and replacement, showing how technological change influences product duration and character. The concept of technical inheritance explains how knowledge and design solutions transfer across generations, illustrated by the evolution of the VW Golf. This process fosters modularity and compatibility, improving repairability and reuse. The circular economy is presented as a framework for reintegrating products, components, and materials into value creation rather than waste. Strategies such as refurbishment, remanufacturing, and recycling are discussed, alongside challenges like downcycling. Material flow management tools, including matrices and Sankey diagrams, visualize return and processing rates and show how design and business-model choices affect circularity outcomes. Energy is introduced as an additional dimension, contrasting production energy with use-phase consumption. Case studies such as laser headlight efficiency demonstrate conversion limits and energy losses, while the shift from fossil to renewable energy emerges as decisive for sustainability. Finally, the information dimension is addressed: the knowledge pyramid, lifecycle databases, IoT systems, and “gentelligent” components illustrate how information enables traceability and reuse, yet also increases digital energy demand, challenging sustainable circularity.