Nanoparticles (NPs) and nanostructured materials (NSMs) have become significant in technological advancements due to their tunable physical, chemical, and biological properties. This review discusses the history, classification, sources, toxicity, and regulations of NMs. NMs are categorized based on size, composition, shape, and origin. The review compares synthetic (engineered) and naturally occurring NPs and NSMs to identify their nanoscale properties and define knowledge gaps in risk assessment. It provides an overview of the history and classifications of NMs, their sources, and toxic effects on mammalian cells and tissues. The review also discusses toxic reactions associated with NPs and NSMs and regulations implemented by different countries to reduce associated risks. NMs are defined as materials with at least one dimension in the range of 1–100 nm. They include carbon-based, inorganic-based, organic-based, and composite-based materials. The classification of NMs based on their dimensions includes 0D, 1D, 2D, and 3D NMs. NMs can be classified as natural or synthetic based on their origin. Natural NMs are found in nature, while synthetic NMs are produced by humans. The history of NMs dates back to ancient times, with examples including Egyptian blue and Roman glass. The development of NMs has led to their use in various applications, including medicine, electronics, and environmental monitoring. Sources of NMs include incidental NMs produced as byproducts of industrial processes, engineered NMs manufactured for specific applications, and naturally occurring NMs found in organisms. Incidental NMs are produced naturally through processes such as volcanic eruptions, forest fires, and cosmic dust. Engineered NMs are produced through various methods, including chemical, physical, and biological synthesis. Naturally occurring NMs are found in microorganisms, plants, insects, and animals. The review highlights the toxic effects of NMs on human health and the environment, as well as the regulations in place to mitigate these risks. It also discusses the potential applications of NMs in various fields, including medicine, electronics, and environmental monitoring. The review concludes that further research is needed to fully understand the risks and benefits of NMs and to develop effective regulations for their safe use.Nanoparticles (NPs) and nanostructured materials (NSMs) have become significant in technological advancements due to their tunable physical, chemical, and biological properties. This review discusses the history, classification, sources, toxicity, and regulations of NMs. NMs are categorized based on size, composition, shape, and origin. The review compares synthetic (engineered) and naturally occurring NPs and NSMs to identify their nanoscale properties and define knowledge gaps in risk assessment. It provides an overview of the history and classifications of NMs, their sources, and toxic effects on mammalian cells and tissues. The review also discusses toxic reactions associated with NPs and NSMs and regulations implemented by different countries to reduce associated risks. NMs are defined as materials with at least one dimension in the range of 1–100 nm. They include carbon-based, inorganic-based, organic-based, and composite-based materials. The classification of NMs based on their dimensions includes 0D, 1D, 2D, and 3D NMs. NMs can be classified as natural or synthetic based on their origin. Natural NMs are found in nature, while synthetic NMs are produced by humans. The history of NMs dates back to ancient times, with examples including Egyptian blue and Roman glass. The development of NMs has led to their use in various applications, including medicine, electronics, and environmental monitoring. Sources of NMs include incidental NMs produced as byproducts of industrial processes, engineered NMs manufactured for specific applications, and naturally occurring NMs found in organisms. Incidental NMs are produced naturally through processes such as volcanic eruptions, forest fires, and cosmic dust. Engineered NMs are produced through various methods, including chemical, physical, and biological synthesis. Naturally occurring NMs are found in microorganisms, plants, insects, and animals. The review highlights the toxic effects of NMs on human health and the environment, as well as the regulations in place to mitigate these risks. It also discusses the potential applications of NMs in various fields, including medicine, electronics, and environmental monitoring. The review concludes that further research is needed to fully understand the risks and benefits of NMs and to develop effective regulations for their safe use.