Carbon quantum dots (CQDs) are a novel form of carbon material with numerous benefits, including adjustable particle size, light resistance, ease of functionalization, low toxicity, excellent biocompatibility, and high water solubility. They have been widely used in various fields such as optoelectronics, bioimaging, drug delivery, cancer therapy, sensors, and environmental remediation. The preparation methods for CQDs are predominantly top-down, such as arc discharge, laser ablation, electrochemical, and chemical oxidation, and bottom-up methods, such as templates, microwave, and hydrothermal techniques. This article provides an overview of the properties, preparation methods, raw materials, and heteroatom doping of CQDs, and summarizes their applications in various fields. The latest research progress in synthesis and application, as well as the challenges outlined in this review, can help and encourage future research on carbon quantum dots.Carbon quantum dots (CQDs) are a novel form of carbon material with numerous benefits, including adjustable particle size, light resistance, ease of functionalization, low toxicity, excellent biocompatibility, and high water solubility. They have been widely used in various fields such as optoelectronics, bioimaging, drug delivery, cancer therapy, sensors, and environmental remediation. The preparation methods for CQDs are predominantly top-down, such as arc discharge, laser ablation, electrochemical, and chemical oxidation, and bottom-up methods, such as templates, microwave, and hydrothermal techniques. This article provides an overview of the properties, preparation methods, raw materials, and heteroatom doping of CQDs, and summarizes their applications in various fields. The latest research progress in synthesis and application, as well as the challenges outlined in this review, can help and encourage future research on carbon quantum dots.