MXenes belong to the class of two-dimensional (2D) transition metals carbides or carbonitrides with the general formula of M n+1 X n T x (n = 1-4), where M stands for a transition metal, X for carbon and/or nitrogen, and T for surface termination groups (e.g., -OH, -O, and -F). 2D MXene nanosheets are synthesized by the selective removal of metal atoms (e.g., Al) from precursor materials that belong to a large family of layered carbides/nitrides called MAX phases. The wide range of possible compositions and rich surface chemistry distinguishes MXenes from other commonly studied 2D materials such as graphene and transition metal dichalcogenides. In the past few years, experimental studies of the physical and chemical properties of various MXenes have revealed their great promise for a broad spectrum of applications including electrochemical energy storage, flexible and transparent electronics, chemical and biosensing applications, water desalination and purification, electromagnetic shielding, and catalysis. Despite their intriguing performance, rapid degradation limits the practical applications of MXenes.