Solar cell~ and solar cell module~ have to be tested for their performance, i.e. their ability to produce electrical power under well-defined conditions of illumination and temperature. The need for performance measurements arises at various stages of development, design and production from different requirement~: at the development level, the main objective is to as~ess the performance of a new concept in comparison with state-of-the-art competitors; at the design level, performance data are required as input for the ~izing and dimensions of photovoltaic ~y~tem~ operating under certain environmental conditions; at the produc- tion level, the cells and modules must be acceptance te~ted against a set of specifications in order to separate deliverables from reject~. For accurate performance measurements and calibration, several methods exist which can be generally categorised into two clas~e~: outdoor methods in natural sunlight, and indoor method~, u~ing ~imulated ~unlight or indirect analytical method~. Depending on the purpose of a performance test, each of these method~ can offer specific advantage~. Therefore, the various methods are not to be looked at as competing, but rather as complementary tool~ for the achievement of accurate electrical performance measurement~.