In the context of a paradigm shift towards a sustainable society based on the circular economy, the exploration of new competitive sources of renewable and eco-friendly energy is a must. Large amounts of waste are produced worldwide, generating negative impacts on the environment. The waste can be used to create valuable products such as biofuels, thus promoting the circular economy, which aligns with the United Nations Sustainable Development Goals (SGDs) 6, 7, 9, 11 and 13. In this chapter, biogas from anaerobic digestion of organic waste is presented as a clean and renewable form of energy that could replace conventional energy sources (fossil fuels, oil, etc.). First, a brief introduction to the fundamentals of anaerobic digestion is given, including parameters affecting the process, reactor technologies, and process monitoring and control. Then, the main substrates suitable for biogas production (i.e., agricultural waste, municipal organic waste including sewage and OFMSW, and industrial waste) are described as well as the main pre-treatments for enhancing biogas production for substrates that are difficult to degrade. Finally, the technology is analysed from an economic and environmental point of view, and challenges and future perspectives of the technology are discussed.