Gold nanoparticles (AuNPs) are newly explored nanoscale materials that possess numerous advantages over the conventional materials due to their novel optical, chemical, and biological properties. Widely applied in biosensing, imaging, and targeted drug delivery because of their localized surface plasmon resonance (LSPR) property, they hold significant value in medicine and diagnostics. The shape, and stability of nanoparticles can be precisely controlled by various synthesis methods, including chemical, physical, and green synthesis, to optimize their functional performance. The use of plant extracts and microorganisms in green synthesis eliminates the need for toxic substances, thereby reducing waste and enhancing the biocompatibility of the resulting nanoparticles. However, challenges remain, including limited scalability, lack of reproducibility, and environmental safety concerns. Recent advancements in microfluidics, artificial intelligence-driven optimization, and hybrid nanomaterials are addressing these issues, unlocking their potential for industrial applications. This chapter highlights the role of AuNPs in advancing sustainable nanotechnology, precision medicine, and environmental remediation. It also discusses the development of AuNPs and various synthesis methods, with particular emphasis on green synthesis and its critical contribution to the progression of sustainable nanotechnology.