<p>Gold nanoparticles (AuNPs) have garnered significant interest in nanomedicine and have emerged as a versatile tool in oncology due to their unique physical, chemical, and optical properties. These characteristics enable applications in both cancer diagnosis and therapy. Recent advancements in green synthesis techniques have introduced eco-friendly and cost-effective alternatives to conventional methods, reducing the use of toxic chemicals and enhancing the biocompatibility of AuNPs. Green synthesis leverages natural agents—such as plant extracts, microorganisms, and biomolecules—as reducing and stabilizing agents. Surface modification and functionalization are essential to improving the stability, solubility, biocompatibility, and targeting efficiency of AuNPs. Capping agents and linkers play pivotal roles in preventing aggregation, prolonging circulation time, and enabling the conjugation of therapeutic or diagnostic molecules. The selection of appropriate capping agents (e.g., PEG, proteins, thiols) and linkers (e.g., EDC/NHS, thiol, disulfide) is critical for achieving desired targeting and therapeutic effects. This review aims to present the latest advancements in the green synthesis and surface engineering of gold nanoparticles, with a special focus on the roles of capping agents and linkers in enhancing their biomedical performance. The objective is to highlight how these innovations are offering promising avenues for the development of multifunctional theranostic platforms in cancer treatment—potentially integrating precise drug delivery, advanced imaging, and photothermal/photodynamic therapies, though these remain largely under preclinical investigation. </p> Graphical Abstract <p></p>