Methanogens are unique prokaryotes critical in the carbon cycle and environmental sustainability. This book offers a comprehensive examination, spanning from the role of methanogens in the gut microbiota to their applications in biotechnology and energy production. It explores how methanogens contribute to digestion, immune regulation, and even the gut-brain axis, focusing on their effects on gastrointestinal and neurological health. Beyond their biological significance, the book highlights the transformative potential of methanogens in industrial applications. It discusses their role in renewable energy production and the integration of methanogens into sustainable energy systems, emphasizing how they help reduce environmental impacts. Based on the latest research, this work is a valuable resource for researchers, professionals, and anyone interested in microbiology, biotechnology, energy, and environmental sciences. Its in-depth analysis makes it an essential reference for those looking to explore the significant scientific and industrial impact of methanogens. Additionally, the book covers the genetic mobility mechanisms in methanogens. It examines the role of genetic elements, such as transposons, in enhancing the adaptability of these microorganisms to environmental changes. Hydrogen and methane co-production potential through anaerobic digestion in energy systems is also explored.