Two-dimensional topological insulators (2DTIs) have attracted increasing attention during the past few years. New 2DTIs with increasing larger spin–orbit coupling (SOC) gaps have been predicted by theoretical calculations and some of them have been synthesized experimentally. In this review, the 2DTIs, ranging from single element graphene-like materials to bi-elemental transition metal chalcogenides (TMDs) and to multi-elemental materials, with different thicknesses, structures, and phases, have been summarized and discussed. The topological properties (especially the quantum spin Hall effect and Dirac fermion feature) and potential applications have been summarized. This review also points out the challenge and opportunities for future 2DTI study, especially on the device applications based on the topological properties.