Textbook in PDF format The concern about using organic waste as a renewable energy source is a critical worldwide issue. In this area, anaerobic digestion (AD) seems to be a promising solution because of the significant reduction of waste quantity and generation of valuable products such as biogas, regarded as being a good energy carrier and digestate with high nutritional potential for agriculture. The current trends in AD focus on improving the efficiency of the process to make this a cost-effective treatment. Depending on the source (agricultural, municipal, or industrial), organic waste varies considering both its composition and structure, and thus the bioaccessibility and biodegradability