Solid-State Lighting (SSL) applications are slowly but gradually pervading into our daily life. An SSL system is composed of an light-emitting diode (LED) engine with a microelectronic driver(s) in a housing that also supplies the optic design. Knowledge of system-level reliability is crucial for the business success of future SSL systems, and also a very scientific challenge. In practice, a malfunction of the system might be induced by the failure and/or degradation of the subsystems/interfaces. Extra costs, in terms of exceed efforts/designs/parts, have been applied to the systemin order to secure the guaranteed reliability performance of SSL system. Most SSL system designs allow few failures of the subsystem/interface during the application period. Hence, a significant cost reduction can be achieved when the system-level reliability is well understood by proper experimental and simulation techniques. This chapter covers the reliability of total SSL systems including the reliability theories and practices for all (sub) components, such as LED engines, drivers, and fixtures.