Energy in the 21st Century is a valuable source of information for students, decision makers, opinion leaders, and the general public. Oil and natural gas price volatility continue to affect both the supply and demand for energy. Advances in other technologies, such as nuclear, wind, solar, and tidal technology, are altering the comparative economics of competing energy sources. New government policies are changing the landscape of the global energy marketplace. From our reliance on fossil fuels to the quest for new sources of energy, Energy in the 21st Century provides a fact-based analysis of the most prominent energy issues of our time. The fourth edition updates data and includes more discussion of recent advances. Some of the highlights of the fourth edition are expanded discussion of climate change and anthropogenic climate change; the 2015 Cop21 Paris Agreement on Climate Change; nuclear fusion reactor prototypes (tokomak Iter and stellarator W7-X); advances in solar thermal and solar photovoltaic power plants, space based solar power, transparent photovoltaic cells, and hybrid solar wind technology; tidal and wave energy converters; oil from algae; the Eu Supergrid; the Goldilocks Policy for energy transition and the Grand Energy Bargain. Energy in the 21st Century has been used as the text for the general college student population, as well as energy overview for Mba students. Pedagogical material includes learning objectives at the beginning of each chapter, end of chapter activities, a comprehensive index, a glossary, and an Appendix to help with converting units. Points to Ponder are provided throughout the text and are designed to encourage the reader to consider material from different perspectives.