Most renewable energy systems lead to the production of “green” electricity and/or heat. Biomass is the most versatile renewable energy source that can be converted, not only to heat and power, but also to fuels. This course focuses on biomass and its thermochemical and biochemical conversion to alternative fuels. The main physicochemical and combustion properties of biofuels are introduced. Hydrogen production and utilization are also included. Special emphasis is given on the sustainability of alternative fuels and methodologies for their environmental assessment.