<p>Anaerobic digestion (AD) is a widely adopted biotechnology for the treatment of organic waste and the simultaneous production of biogas. However, the efficiency of this process is often limited by factors such as slow hydrolysis, microbial inhibition, and process instability. In recent years, the incorporation of nanoparticles (NPs) has emerged as a promising strategy for enhancing AD performance. This review critically examines the role of various NPs including metallic NPs (e.g., Fe, Ni, Ag), metal oxides (e.g., Fe₃O₄, ZnO, TiO₂), and carbon-based nanomaterials in improving key stages of the AD process. The mechanisms of action, such as microbial stimulation, enzymatic activity enhancement, improved electron transfer, and toxicity mitigation are discussed in detail. Furthermore, the review addresses the influence of NP type, concentration, size, and dosing strategy on biogas yield, methane content, and overall system stability. Potential challenges, including NP toxicity, accumulation, and environmental implications, are also considered. Finally, research gaps and future perspectives are highlighted to guide the development of safe, efficient, and scalable nanotechnology applications for AD systems.</p> Graphical Abstract <p></p>