Electrochromic device testing and durability is discussed in this study. This work begins with a discussion of performance criteria for switchable glazings used in building applications. This is followed by device design of several common electrochromic device types. The types are distinguished by structure and electrolyte type. A number of test methods are used for the analysis of electrochromic devices. Device lifetime and degradation covers considerable work on amorphous tungsten oxide. Some degradation and ageing modes are identified for electrochromic devices during static and cyclic testing. The degradation modes are film dissolution, transparent conductor etching, gas generation, humidity dependence, secondary reactions and photoreactions. Many of these mechanisms are specific to the materials, device design, and the operating conditions used. Overall, future of electrochromic devices looks very promising, but there are many issues in this study that designers need to take into consideration for electrochromic glazings.