This book includes select proceedings of the International Conference on Advances in Sustainable Solutions for Energy Transitions (ASSET 2025), organized by the School of Energy Science and Engineering at the Indian Institute of Technology (IIT) Guwahati, India from January 2 to 4, 2025. This volume provide a comprehensive coverage of major areas in sustainable energy generation, including biomass and biofuels, hydrogen energy, and biomass-derived chemicals. It features a wide range of research contributions spanning diverse energy themes and highlights recent advancements in biohydrogen production, biomass-based chemical processes, and clean fuel technologies. Together, these contributions offer an integrated overview of current research progress, emerging technologies, and practical applications that are expected to play a significant role in shaping future sustainable energy transitions. This book will be especially valuable for researchers, postgraduate students, industry practitioners, policy makers, technology developers, and academic institutions involved in renewable energy and sustainability, energy system design, clean technology deployment, and transition planning.