Nanoparticles are nanoscale structures characterized by a high surface area-to-volume ratio, which imparts distinctive physicochemical properties. Their small size (typically below 100 nm) and the ability to modify their surface enable their application across diverse fields. The properties and functional performance of nanoparticles are influenced by several factors, including synthesis techniques as well as physical characteristics such as size, shape, and morphology. Furthermore, the choice of material used in nanoparticle fabrication plays a crucial role in determining their suitability for specific applications. Based on their composition, nanoparticles are broadly categorized into organic, inorganic, and carbon-based types. These groups encompass a wide range of materials, including polymers, proteins, lipids, metal ions, and magnetic substances. Each material type exhibits distinct features that govern the behaviour, efficiency, and potential toxicity of the nanoparticles. As a result, specific nanoparticles are preferentially utilized in particular applications where their performance and safety profiles are optimized. Therefore, both the classification and material selection are critical considerations in nanoparticle research and practical use. This paper presents a comprehensive overview of nanoparticle classifications, highlights key materials within each category, and discusses their respective application domains. Additionally, it examines the associated toxicity aspects, providing an integrated perspective on nanoparticle materials and their relevance in various fields.