The concept of open quantum system is of fundamentalimportance to many fields of modern physics. In particular, the energydissipation and particle exchange between the system of primary interest andsurrounding environment are the keys to many fascinating quantum phenomena. Inthe special topic “Progress in OpenQuantum Systems: Fundamentals and Applications”, severalstate-of-the-art quantum dissipation theory methods are introduced. Theusefulness and practicality of these methods are highlighted through a widerange of applications including energy transfer, electron and heat transport,and exciton diffusion. [Photo credits: Xiao Zheng, University of Science andTechnology of China; Yun-An Yan, Guizhou Education University]