Fighting global warming is urgent problem in the world now. This chapter describes the significance of preventing global warming. Effective utilization of biomass is one of the very important pathways for renewable energies. Among biofuels such as biochar, biodiesel, ethanol, producer gas, biogas, etc. this book focuses on biogas. Biogas is produced through anaerobic digestion (AD) process. Purified and upgraded biogas is used for producing high quality methane for injection in natural gas pipelines and engines. Biogas has been used in both, spark ignition engines and dual-fuel engines. It is important to utilize biogas engines for producing electricity and heat because biogas is suitable to local production for local consumption. Internal combustion engines are considered as important systems for conversion of chemical energy contained in biogas to power and electricity. The engine technologies have been developed and improved for a century. This book covers characteristics of combustion and exhaust emissions in spark ignition engines and dual-fuel engines fueled with biogas, as well as several new engine combustion technologies which can be applied to biogas engines.