This article provides a comprehensive review of nanoparticles (NPs), focusing on their classification, applications, and toxicity. Nanoparticles, with sizes up to 100 nm, exhibit unique properties due to their high surface area-to-volume ratio, making them valuable in various fields. The article categorizes NPs into three main types: organic, inorganic, and carbon-based, each with distinct characteristics and applications. Inorganic NPs, such as magnetic, ceramic, and semiconductor NPs, are widely used in biomedical applications, including drug delivery, imaging, and therapeutic treatments. Magnetic NPs, for instance, are used in magnetic resonance imaging (MRI) and magnetic hyperthermia. Ceramic NPs, like hydroxyapatite and silica, are employed in drug delivery and tissue engineering due to their stability and biocompatibility. Semiconductor NPs, such as zirconium dioxide and zinc oxide, are used in catalysis, sensors, and biomedical applications. Carbon-based NPs, including graphene, fullerenes, carbon black NPs, and carbon quantum dots, are valued for their high chemical stability, electrical conductivity, and optical properties. Graphene and its derivatives are used in drug delivery and biosensors, while fullerenes are utilized in antioxidants and photothermal therapy. Carbon black NPs are employed in industrial applications, though their potential toxicity limits their use in biological systems. Carbon quantum dots are promising for bioimaging and sensing due to their low toxicity and fluorescence properties. Organic NPs, such as polymeric, lipid-based, and carbohydrate NPs, are biodegradable and biocompatible, making them suitable for drug delivery and biomedical applications. Polymeric NPs, like chitosan and alginate, are used in targeted drug delivery and antimicrobial applications. Lipid-based NPs, including liposomes, solid lipid NPs, and nanostructured lipid carriers, are effective in delivering both hydrophilic and lipophilic drugs. Carbohydrate NPs, such as starch and dextran, are used in food, pharmaceuticals, and cosmetics. The article also discusses the toxicity of NPs, emphasizing the importance of understanding their potential risks to ensure safe and effective applications. Overall, the review highlights the diverse applications of NPs across various fields and underscores the need for further research to optimize their use while minimizing toxicity.This article provides a comprehensive review of nanoparticles (NPs), focusing on their classification, applications, and toxicity. Nanoparticles, with sizes up to 100 nm, exhibit unique properties due to their high surface area-to-volume ratio, making them valuable in various fields. The article categorizes NPs into three main types: organic, inorganic, and carbon-based, each with distinct characteristics and applications. Inorganic NPs, such as magnetic, ceramic, and semiconductor NPs, are widely used in biomedical applications, including drug delivery, imaging, and therapeutic treatments. Magnetic NPs, for instance, are used in magnetic resonance imaging (MRI) and magnetic hyperthermia. Ceramic NPs, like hydroxyapatite and silica, are employed in drug delivery and tissue engineering due to their stability and biocompatibility. Semiconductor NPs, such as zirconium dioxide and zinc oxide, are used in catalysis, sensors, and biomedical applications. Carbon-based NPs, including graphene, fullerenes, carbon black NPs, and carbon quantum dots, are valued for their high chemical stability, electrical conductivity, and optical properties. Graphene and its derivatives are used in drug delivery and biosensors, while fullerenes are utilized in antioxidants and photothermal therapy. Carbon black NPs are employed in industrial applications, though their potential toxicity limits their use in biological systems. Carbon quantum dots are promising for bioimaging and sensing due to their low toxicity and fluorescence properties. Organic NPs, such as polymeric, lipid-based, and carbohydrate NPs, are biodegradable and biocompatible, making them suitable for drug delivery and biomedical applications. Polymeric NPs, like chitosan and alginate, are used in targeted drug delivery and antimicrobial applications. Lipid-based NPs, including liposomes, solid lipid NPs, and nanostructured lipid carriers, are effective in delivering both hydrophilic and lipophilic drugs. Carbohydrate NPs, such as starch and dextran, are used in food, pharmaceuticals, and cosmetics. The article also discusses the toxicity of NPs, emphasizing the importance of understanding their potential risks to ensure safe and effective applications. Overall, the review highlights the diverse applications of NPs across various fields and underscores the need for further research to optimize their use while minimizing toxicity.