In this talk, I will review the recent progress on time-reversal invariant topological insulators in two and three dimensions. In two dimensions, the time-reversal invariant topological insulator is known as quantum spin Hall insulators, which has a bulk gap and robust gapless edge states protected by time-reversal symmetry. The quantum spin Hall insulator is theoretically predicted to realize in two semiconductor quantum wells: type-III quantum well HgTe/CdTe and broken-gap type-II quantum well InAs/GaSb. The prediction in the first material has soon been confirmed experimentally. As a consequence of the nontrivial topology, we have shown that a magnetic domain wall on quantum spin Hall edge traps a half electron charge. Soon after its discovery, the three dimensional generalization of quantum spin Hall insulator is proposed theoretically. Two classes of materials are proposed as candidates of three dimensional topological insulators: BixSb1-x alloy and Bi2Se3, Bi2Te3, Sb2Te3. Experimental evidences of surface states have been observed for both classes. We show that the three dimensional topological insulators are characterized by the topological magneto-electric effect, corresponding to an ExB term in the free energy. Due to this effect, the surface of a three-d topological insulator acts as a "magic mirror", from which the image of an electron is a magnetic monopole. An electron associated with its image monopole realizes the composite particle "dyon" proposed in high energy physics and has fractional statistics.