The book Biogas in the 21st Century - Developments and Perspectives provides an overview of the significance of biogas within the current and global energy framework, addressing crucial topics relevant to today's evolving energy systems and promoting worldwide sustainable development. This edited volume explores the latest advances in biogas production for multipurpose industrial applications and the production of green hydrogen. Moreover, key challenges and new perspectives are discussed, including risks related to the formation of hydrogen sulphide (H2S) during biogas production and the potential of third-generation biogas for energy production from algae. Additionally, the book offers a global overview of the pivotal role of biogas in advancing the decarbonization of existing energy systems by reducing waste, promoting a circular economy, and creating bioclimatic and sustainable homes. This comprehensive resource is ideal for scholars, stakeholders, policymakers, and professionals, as it delivers valuable insights into the current and future directions of biogas utilization.