Numerous laws – including the Green New Deal – have been proposed or passed in cities, states, and countries to transition from fossil fuels to 100% clean, renewable energy in order to address climate change, air pollution, and energy insecurity. This textbook lays out the science, technology, economics, policy, and social aspects of such transitions. It discusses the renewable electricity and heat generating technologies needed; the electricity, heat, cold, and hydrogen storage technologies required; how to keep the electric power grid stable; and how to address non-energy sources of emissions. It discusses the history of the 100% Movement, which evolved from a collaboration among scientists, cultural leaders, business people, and community leaders. Finally, it discusses current progress in transitioning to 100% renewables, and the new policies needed to complete the transition. Online course supplements include lecture slides, answers to the end-of-chapter student exercises, and a list of extra resources.