 The increasing complexity of energy systems has created a need for improved methods of analysis and optimization. This paper reviews several existing models and their applications, including those related to GHG emissions mitigation, energy systems planning under uncertainty, and model-based decision support tools. The paper also highlights the importance of data reliability, uncertainty, post-modeling analysis, and the development of simulation techniques. This article was authored by Jing Dai, Guahua Wang, Yang Zeng, and others.