The chapter examines product lifetime as a key lever for sustainability, linking policy, market, and engineering strategies to counter obsolescence. Policy measures include EcoDesign lifetime requirements, extended warranties, and spare-part access, with France’s ban on deliberate obsolescence marking a precedent—while safety must scale with longevity. Reliability is analysed statistically via survival probability, bathtub curves, and MTBF or MTTF, supported by methods such as fault and event trees, FMEA, HALT, and EOL testing that translate component data into system-level risk control. Software reliability differs, depending on latent defect discovery rather than physical ageing. A design toolkit (covering architecture choices, redundancy, fail-safety, proven parts, testability, and data-driven monitoring) extends lifetime while balancing cost and availability. Maintenance strategies (reactive, preventive, and predictive) differ in cost, downtime, and risk, structured by DIN 31051 into maintenance, inspection, repair, and improvement. Continuous improvement, rooted in Kaizen and ISO 9001, feeds field insights into upgrades through patches, better materials, and modular replacements. Linking lifetime to circularity, the Material Circularity Indicator (MCI) highlights durability and reparability as superior to recycling alone. The Upgrade Factory concept envisions industrial refurbish-and-upgrade loops that return products to market, tackling obsolescence and promoting the “eternal product.”