Carbon quantum dots (CQDs) have emerged as a highly promising class of carbon-based nanomaterials duetotheirexceptional optical properties, tunable surface chemistry, and excellent biocompatibility. Since their discovery in 2004, CQDshavegained considerable attention as sustainable alternatives to traditional semiconductor quantum dots, which oftencontaintoxicheavy metals. Their nanoscale size (<10 nm) induces quantum confinement effects that lead to strong andtunablephotoluminescence, excitation-dependent emission, upconversion fluorescence, and remarkable photostability. Additionally, thepresence of abundant surface functional groups enhances solubility, chemical reactivity, and facilitates easy functionalizationfortargeted applications. Recent advances in CQD synthesis—including hydrothermal, microwave-assisted, greenbiomass-basedroutes, and emerging techniques such as microreactor-assisted fabrication and heteroatom doping—have enabled bettercontrolover particle size, crystallinity, and quantum yield. Characterization tools such as TEM, XRD, FTIR, Raman spectroscopy, UV–Vis,PL spectroscopy, and XPS play a crucial role in understanding CQD structure, surface states, and optical behavior. CQDshavedemonstrated broad applicability across bioimaging, biosensing, drug delivery, photocatalysis, environmental remediation, energystorage, and optoelectronic devices. Their low cytotoxicity allows safe use in biological systems, while their electron-transfercapabilities make them highly effective in sensing and catalysis. Despite these advantages, challenges remain regardingsynthesisreproducibility, large-scale production, and incomplete understanding of photoluminescence mechanisms. Overall, CQDsrepresent an important class of next-generation nanomaterials with significant potential for multidisciplinary applications.Continued advancements in synthesis, surface engineering, and mechanistic understanding are expected to further enhancetheirperformance and enable widespread technological adoption.