An in situ process monitor for the CuInxGa1?xSe2 (copper indium gallium selenide) (CIGS) coating system is a very important tool that produces repeatable, high-quality CIGS coatings. This letter provides an overview of the current state of application of in situ process monitor systems for co-evaporation CIGS coatings. A comparison between different in situ monitoring systems is given and a novel multiple-elements rate monitor system is introduced.