This review aims to briefly discuss about the research progress of the dynamics of binary droplet collision in gaseous environment, with emphasis on revealing the multi-scale, multi-physics, and nonlinear characteristics of the problem. First, we reviewed the previous experiments on binary droplet collision in various gases of sub-and super-atmospheric pressures. Second, we highlighted several theoretical models accounting for coalescence, bouncing, and separation of identical droplets. Finally, we discussed the recent studies on droplet coalescence and subsequent mixing, and non-Newtonian droplet collision, which have been gained increasing interests.