 Two-dimensional, 2D materials have attracted significant interest due to their unique physical properties such as optical, electric, mechanical and magnetic. The combination of these materials into heterostructures has provided new opportunities for exploration of novel physics which cannot be accessed in single 2D materials or three-dimensional, 3D heterostructures. Recent advances in the synthesis of high-quality 2D heterostructures have enabled the fabrication of various heterostructure devices with remarkable performances. These include tunneling transistors, photodetectors and spin-tronics devices. This review summarizes recent developments in the fabrication, properties and applications of 2D heterostructures, followed by discussion of current challenges and future prospects. This article was authored by Yen Ping Lu, C.U. Zhang, Jun He and others.