Gold nanoparticles (AuNPs) are of great interest due  to their novel optical, chemical, and biological properties, and have found broad utility in a variety of applications. In biomedicine, AuNPs enhance diagnostic methods, deliver drugs to specific targets, and act as photothermal agents for improving the precision of cancer treatment. The strong surface plasmon resonance (SPR) of AuNPs enables rapid biosensing and real-time detection of diseases. AuNPs are also employed in the environmental applications as catalyst for pollutants degradation, enhancers of air and water purification, and sensors for the sensitive detection of heavy metals and toxic substances. AuNPs are used in nano-fertilizers formulations to stimulate plant growth, in disease diagnostics, and across a range of agriculture applications. Catalysis, flexible electronics, and surface enhanced Raman spectroscopy (SERS) are some of the industrial and technological applications of AuNPs. Based on emerging trends, AuNPs are being integrated into smart materials, nanotheranostics, and hybrid nanostructures, which are representative of future-generation innovations for sustainability, precision medicine, and environmental protection. This chapter underscores the substantial potential of AuNPs across multidisciplinary applications, highlighting their transformative impact on diverse sectors including health, industry, agriculture, and the environment.