Prof. Xiao-Gang Wen was cited for his creative contributions to theoretical condensed matter physics in the area of strongly correlated systems, in particular, in the theory of high Tc superconductors and fractional quantum Hall effect. In a classical paper with Wilczek and Zee, he provided the first systematic formulation of the chiral spin liquid state, a novel candidate ground state for the strong correlation model of the high Tc superconductors. His most influential work lies in the area of fractional quantum Hall effect. He was the first to recognize that the edge excitation in a quantum Hall state is an example of the chiral Luttinger liquid. He showed how the study of the edge state can distinguish between the topological order of the different quantum Hall states. He proposed concrete experimental tests of his ideas and theoretical predictions. His work has stimulated much theoretical activities and experimental work as well.