This chapter provides a comparison of the suitability of different renewable sources for future energy production. Specifically, four criteria, available capacity, safety, greenhouse gas emissions and cost are considered for the renewable energy resources discussed in Chaps. 3 and 4 : solar, hydroelectric, wind, geothermal and biofuels. Installed capacities are summarized and the possibility of expanding these facilities is discussed. Safety, as determined by deaths per unit energy generated, is low for all renewables except biofuels, which contribute to air pollution. All renewable energy sources produce less greenhouse gas emissions than fossil fuels, however, biofuels produce the most due to emissions during combustion. The cost of electricity generated by hydroelectric, wind, geothermal and biofuels has, traditionally been similar to that from fossil fuel generation. In recent years the cost of solar power has decreased dramatically. Photovoltaic power is now comparable to fossil fuels, although, electricity from concentrating solar technologies is still more expensive.