[en] Like any other electrical equipment insulation, insulation systems of a rotating machine also need to meet operating requirements such as thermal, electrical, chemical and environmental nature. The electrical insulation system, being less robust than the mechanical component, is the most vulnerable part that undergoes ageing when exposed to the complex stress environment during its operation. The innovation in the insulation system of the rotating machine has come in terms of development of better insulating materials, manufacturing process and evaluation technique during manufacture and on the end product. This paper covers an overview of the specific requirement of insulation system vis-a-vis development in the insulation material, testing and monitoring methods. (author)