C-dots (carbon dots) are a novel class of carbon-based spherical nanomaterials with diameters less than 10 nm. They are present in the nature and have been found in honey and beer. With abundant laboratory techniques, c-dots have also been synthesized with diverse carbon-based precursors. The synthetic approaches of carbon dots are generally divided into top-down and bottom-up approaches mediated by hydrothermal/solvothermal, microwave, ultrasonication, laser ablation and arc discharge. In recent years, carbon dots gradually draw much attention due to their unique properties and numerous promising applications.