An issue in engineering design is a system's design lifetime. Economists study durability choice problems for consumer goods but seldom address lifetime problem(s) of complex engineering systems. The issues for engineering systems are complex and multidisciplinary and require an understanding of the 'technicalities of durability' and the economic implications of the marginal cost of durability and value maximization. Commonly the design lifetime for an infrastructure is set between 30 and 70 years. Satellite lifetimes are also assigned arbitrarily or with limited analysis. This book provides a systemic qualitative and quantitative approach to these problems addressing, first, the technicality of durability, second, the marginal cost of durability, and third, the durability choice problem for complex engineering systems with network externalities (competition and market uncertainty) and obsolescence effects (technology evolution). Since the analyses are system-specific, a satellite example is used to illustrate the essence and provide a quantitative application of said analyses.