Anaerobic digestion is a complex biological process studied extensively in research, involving the breakdown of organic matter by microbial consortia in the absence of oxygen to produce biogas and digestate. As a research concept and methodological approach, it investigates the underlying microbial ecology, biochemical reaction pathways, and kinetic parameters governing the conversion of diverse organic substrates into simpler compounds and ultimately methane and carbon dioxide. Key characteristics include its multi-stage nature (hydrolysis, acidogenesis, acetogenesis, methanogenesis) mediated by distinct microbial functional groups operating under strictly anoxic conditions. Its significance lies in its application as a sustainable technology for waste valorization, renewable energy generation (biogas), and nutrient recycling (digestate) within the framework of a circular bioeconomy.