Nanoparticles or nanostructured materials are categorized as those within the size of several hundreds of nanometres, having at least one dimension in the nanoscale, depending on the type. Over the last decade, the trial and application of nanoparticles has been tremendous in the fields of healthcare, manufacturing/catalysis, environment and consumer goods. A variety of structural types ranging from inorganic to organic and hybrid nanomaterials has been designed, which use more than one route of synthesis. Materials synthesized by different routes may be used for similar applications, depending on the reproducibility in terms of size and shape. Two general approaches in the synthesis of nanomaterials are bottom-up and top-down. Bottom-up approaches comprise nucleation and self-assembly from molecular dimensions either in the liquid or the vapour phase, while top-down approaches involve mechanical grinding, high pressure deformations and surface erosion. The necessary parameters that define a proper nanostructured material in bulk are their identical size, identical morphology, being monodispersed and having the same composition. Nanoparticles of any type being metastable clusters tend to aggregate. Hence, simultaneous surface modification of nanoparticles remains a prerequisite. The purpose of this chapter is not to summarize all the results reported in the literature, but to give a thorough understanding of the ongoing chemical processes in each method. Hence, it focuses on the major routes of chemical synthesis and capping routes of various types of organic–inorganic nanoparticles (mainly metallic, polymeric and magnetic) for diverse applications. Detailed properties and functional mechanisms of them for various applications are not within the scope of the chapter.