MXenes have received extensive attention from scholars due to their unique layered structure, significant electrical conductivity, and excellent mechanical properties. In addition to their pristine forms, they could also be incorporated with other components for attaining hybrids and nanocomposites, accompanying with amplified functionalities. It has been widely used in lithium batteries, supercapacitors, electromagnetic shielding, tumor therapy, biosensors, photocatalysis, and other fields, and has shown great application potential in energy conversion and storage. The purpose of this article is to encyclopaedically overview the latest progress in synthesis and characterization of MXenes, while their potential applications in energy conversation such as water splitting and solar cells, as well as in energy storage such as Li-ion batteries, supercapacitors, and hydrogen energy will be comprehensively elaborated. Development opportunities and challenges are summarized.