With the recent advancement in nanotechnology, nanoparticles (NPs) offer an ample variety of smart functions than conven-tional materials in various aspects. As compared to larger particles, NPs possess unique characteristics and excellent abilities, such as low toxicity, chemical stability, surface functionality, and biocompatibility. These advantageous properties allow them to be widely utilized in many applications, including biomedical applications, energy applications, IT applications, and industrial applications. In order to fulfill the increasing demands of NP applications, existing NP synthesis methods need to be improved based on the requirements of different applications to further their usage. A comprehensive understanding of the relationships between synthesis parameters and properties of NPs can help us better fine-tune them with designed properties and minimal toxicity. This review paper will discuss the commonly used synthesis methods of functionalized NPs, as well as future directions and challenges to develop various synthesis methods further.