Gold nanoparticles (AuNPs) are currently among the most well-known nanomaterials, with numerous applications in medicine, catalysis, and environmental sciences, and other fields. Their synthesis has been achieved through physical, chemical, and biological methods, each differing in mechanism and requirements. Physical preparation techniques such as laser ablation and evaporation–condensation can produce high-purity AuNPs, but they require expensive and sophisticated equipment. The Turkevich–Frens and Brust–Schiffrin methods are examples of chemical synthesis techniques. These methods offer precise control over nanoparticle size and stability, which is particularly important in biomedical  applications. Green synthesis, which utilizes plant extracts and microorganisms, provides a sustainable alternative that generates minimal or no toxic waste, making it suitable for biological systems. The size, shape, and stability of AuNPs are influenced by the synthesis parameters such as pH, temperature, and reagent concentration. However, challenges remain, including limited scalability, poor reproducibility, and potential environmental impact. Promising innovations to address these issues include  microfluidics, artificial intelligence driven optimization, and the development of hybrid nanomaterials. This chapter will also highlight the various sources of AuNPs and their synthesis methods, with a focus on sustainable approaches and their implications for the future of nanotechnology and industry.