As a society we use energy for climate control and lighting in buildings, moving people and goods form one place to another and making things. Our standard of living depends on transforming energy locked up in fossil fuels, atomic nuclei or provided free of charge by the sun and wind into a form that we can use. This book uses simple classical physics (mechanics, thermodynamics and electromagnetism) to quantitatively review sources of energy and how we use them. It addresses key questions such as: Can renewables such as solar and wind take over from fossil fuels? How much will their use reduce CO2 emissions?