Human civilization has long relied on fire from biomass for energy. Burning, an oxidation reaction, liberates energy and continues until the material reaches its highest oxidation state. The evolution of energy sources, from forest fires to nuclear fuels, marks significant progress. Understanding fuel types and classifications is essential for students and educators. This book covers upstream and downstream processing of various fuels—biomass, petroleum, coal, natural gas, nuclear fuels, hydrogen, and fuel cells—along with combustion technology for energy extraction. It also addresses recent advances, emission concerns from energy industries, and stubble burning. The book explores how advanced formulations of coal, petroleum, and alternative fuels can be optimized for existing combustion systems, ensuring efficiency and compliance with EURO VI emission norms. This comprehensive guide aims to inform readers about fuel classification, energy production, and future research prospects.