With the advent of graphene, more and more two‐dimensional (2D) materials, such as graphene oxide (GO), transition‐metal dichalcogenides (TMDs), black phosphorus, transition‐metal carbides and carbonitrides (MXenes), 2D metal‐organic frameworks (MOFs) and 2D covalent organic frameworks (COFs), etc., have been discovered over the past two decades. The atomic thickness and the Van der Waals stacking of these materials endow them with wide application potentials in various fields. One of the intriguing features of 2D materials is their diversified properties caused by either surface functionalization or heteroatom doping. Since the functionalization can greatly alter the surface, interface, electronic and optical properties, it gives rise to the realization of a large family of valuable materials for a broad range of applications, including devices, energy conversion and storage, chemical or photocatalysis. In addition, the nanosized pores or channels formed by either 2D layer stacking (e.g., graphene, GO and MXene) or the intrinsic porosity (e.g., COFs and MOFs) make these materials fascinating candidates for fabrication of high‐performance separation membranes. Thanks to the high selectivity of nanopore (channel) for both molecules and ions, these 2D materials membranes have been widely used in gas separation, organic molecule separation, ion separation as well as separator in energy devices.