Energy has far reaching impact in everyday life, technology, and development. Primary energy sources are extracted or captured directly from the environment, while the secondary energy sources are derived from the primary energy sources, for example, in the form of electricity or fuel. Primary energies are nonrenewable energy (fossil fuels), renewable energy, and waste. Nonrenewable energy resources are coal, petroleum, natural gas, and nuclear, while renewable energy resources are solar, bioenergy, wind, and geothermal. Energy density and the impact of fossil fuels on global warming are discussed briefly.