As the environment of a fault-tolerant system increases in complexity, the system’s performance may be degraded if it has to respond to all conditions in the service range at any time. The performance may be improved if the system is able to adapt its structure to changing environmental conditions. Adaptation may be valuable not only at run time but over the entire life-cycle. At run time, adaptation should be automatic, but during design and configuration, it may be manually driven. We examine the benefits of adaptation at different times of the life-cycle, and discuss issues of structure and control. We review several architectural approaches to adaptive system design and recommend using reflective architectures because of their power and generality.