Renewable energy refers to the energy that is derived from renewable resources which can be naturally replenished on a human timescale. The energy harnessed from wind, tides, waves, geothermal heat, air and sunlight is renewable. It has applications in transportation, electricity generation, rural energy services, and air and water heating and cooling. In contrast to fossil fuels, renewable energy sources are spread over wide geographical areas, and their rapid deployment can have implications in climate change mitigation, energy security and engendering economic benefits. Today, renewable energy systems are becoming cheaper and more efficient. Renewable energy technologies pertaining to marine energy, cellulosic ethanol and hot-dry-rock geothermal power are also being developed. Innovative designs such as floating solar arrays, artificial photosynthesis using nanotechnology, solar-assisted heat pump, solar aircraft, algae fuels, and similar such renewable energy technologies are also being designed. This book is a compilation of chapters that discuss the most vital concepts and emerging trends in renewable energy. The various advancements in renewable energy technologies are glanced at and their effect in terms of environmental sustainability are looked at in detail. The readers would gain knowledge that would broaden their perspective about renewable energy.