Global resource use and waste generation have been increasing exponentially, motivating efforts toward resource efficiency and circular economy. One promising solution is product lifetime extension, which can potentially reduce the demand for new products and the associated resource use, greenhouse gas emissions, and other impacts. However, longer product lifetimes may involve environmental trade-offs and behavioral rebound effects, calling for a systemic perspective considering the product’s life cycle and the consumer. This thesis investigates the environmental benefits of product lifetime extension by combining industrial ecology methods, i.e., material flow analysis (MFA) and life cycle assessment (LCA), with insights from social approaches to consumption, particularly social practice theories. The thesis contribution includes: 1) creation of a framework for comprehensive modeling of lifetimes in dynamic MFA, 2) development of a model investigating the historical trends in the lifetimes of large domestic appliances in Norway, and 3) environmental impact assessment of product lifetime extension strategies in Norway, exploring the potential of policy for large household appliances and of alternative consumption modes for clothing. The created modeling framework distinguishes two main types of influences on product lifetime: product “nature” (inherent product durability) and “nurture” (external influences, e.g., repair). The framework is useful for studying the effect of changes in product lifetimes on stocks, and flows, which is essential for analyzing policy-relevant circular economy strategies. The investigation of historical lifetimes showed no uniform trend across large domestic appliances, with only washing machines and ovens clearly experiencing a lifetime decrease of around 40% observed in the 1990s-2000s. While the reasons for this decrease are unknown, the consumer practice perspective suggests hypotheses involving changes in laundry practices and in how kitchens are designed and renovated. Finally, the thesis shows that product lifetime extension offers significant potential for environmental savings, particularly if changes in product design (“nature”) and consumer practices (“nurture”) are encouraged by policy, e.g., ecodesign, right-to-repair, and more holistic approaches. Overall, understanding consumer practices and the broader context of consumption was shown to be essential for devising successful lifetime extension policies. A deeper engagement of modelers and policymakers in the consumption context could be helpful in addressing systemic issues and thus accelerate efforts toward resource efficiency and circular economy