This article provides a comprehensive overview of carbon quantum dots (CQDs), focusing on their synthesis, properties, and applications. CQDs, which are small carbon nanoparticles (less than 10 nm in size), have gained significant attention due to their unique properties and potential in various fields. The authors discuss the recent progress in CQD synthesis methods, including chemical ablation, electrochemical carbonization, laser ablation, microwave irradiation, hydrothermal/solvothermal treatment, and confined pyrolysis. They also explore size control techniques and surface modifications to enhance the optical and biological properties of CQDs. The article highlights the luminescent mechanisms of CQDs, including fluorescence, phosphorescence, chemiluminescence, and electrochemical luminescence. Additionally, it reviews the biological properties of CQDs, emphasizing their biocompatibility and low toxicity. Finally, the article discusses the diverse applications of CQDs in biomedicine, optronics, catalysis, and sensors, such as bioimaging, multimodal imaging, and drug delivery.This article provides a comprehensive overview of carbon quantum dots (CQDs), focusing on their synthesis, properties, and applications. CQDs, which are small carbon nanoparticles (less than 10 nm in size), have gained significant attention due to their unique properties and potential in various fields. The authors discuss the recent progress in CQD synthesis methods, including chemical ablation, electrochemical carbonization, laser ablation, microwave irradiation, hydrothermal/solvothermal treatment, and confined pyrolysis. They also explore size control techniques and surface modifications to enhance the optical and biological properties of CQDs. The article highlights the luminescent mechanisms of CQDs, including fluorescence, phosphorescence, chemiluminescence, and electrochemical luminescence. Additionally, it reviews the biological properties of CQDs, emphasizing their biocompatibility and low toxicity. Finally, the article discusses the diverse applications of CQDs in biomedicine, optronics, catalysis, and sensors, such as bioimaging, multimodal imaging, and drug delivery.