Grey system theory was initiated in the beginning of 1980s. Since then the research on theory development and applications is progressing. However, until today nearly all researchers of grey system theory are from Chinese speaking areas, and the theory is still hardly known nor accepted in the western world. The paper addresses the state-of-the-art development of grey system theory and its application. It aims to highlight and analyse relevant issues (i.e. obstacles, possible solutions and potential trends) for further research from the perspective both of grey system theory and of the grey system methods.