This review provides a comprehensive overview of nanoparticles (NPs), focusing on their classification, applications, and toxicity. NPs are defined as nanostructures with sizes up to 100 nm, characterized by high surface area-to-volume ratios and unique properties. They are classified into three main categories: organic, inorganic, and carbon-based, each with distinct materials and applications. Inorganic NPs include magnetic, ceramic, and semiconductor NPs, with magnetic NPs showing promise in biomedical applications like MRI and drug delivery. Ceramic NPs are used in biomedical applications due to their biocompatibility and stability. Semiconductor NPs, such as ZrO₂ and ZnO, are widely used in electronics and biomedical applications. Carbon-based NPs include graphene, fullerenes, carbon black, and carbon quantum dots, each with unique properties and applications in drug delivery, imaging, and sensing. Organic NPs, such as polymeric and lipid-based NPs, are used in drug delivery and biomedical applications due to their biocompatibility and biodegradability. The review also discusses the toxicity of NPs, emphasizing the importance of material selection and surface modifications in determining their safety and effectiveness. Overall, the classification and properties of NPs are crucial for their application in various fields, highlighting the need for further research to optimize their use and minimize potential risks.This review provides a comprehensive overview of nanoparticles (NPs), focusing on their classification, applications, and toxicity. NPs are defined as nanostructures with sizes up to 100 nm, characterized by high surface area-to-volume ratios and unique properties. They are classified into three main categories: organic, inorganic, and carbon-based, each with distinct materials and applications. Inorganic NPs include magnetic, ceramic, and semiconductor NPs, with magnetic NPs showing promise in biomedical applications like MRI and drug delivery. Ceramic NPs are used in biomedical applications due to their biocompatibility and stability. Semiconductor NPs, such as ZrO₂ and ZnO, are widely used in electronics and biomedical applications. Carbon-based NPs include graphene, fullerenes, carbon black, and carbon quantum dots, each with unique properties and applications in drug delivery, imaging, and sensing. Organic NPs, such as polymeric and lipid-based NPs, are used in drug delivery and biomedical applications due to their biocompatibility and biodegradability. The review also discusses the toxicity of NPs, emphasizing the importance of material selection and surface modifications in determining their safety and effectiveness. Overall, the classification and properties of NPs are crucial for their application in various fields, highlighting the need for further research to optimize their use and minimize potential risks.