Solar energy is the power obtained by the conversion of heat and light radiated by sun using techniques such as photovoltaics, solar heating and artificial photosynthesis. It is a renewable source of energy which is also believed to be the cleanest and most abundant renewable energy source. Solar technologies are classified into active and passive solar systems. Active solar systems comprise devices to convert sun's energy into a more usable form such as electricity or hot water. Passive solar techniques do not employ any external electrical or mechanical device and focus on optimizing the use of heat or light directly from the sun. The energy captured using solar devices can be employed for various purposes such as lighting, cooking, heating, transportation, etc. This book traces the progress of this field and highlights some of its key concepts and applications. It will also provide interesting topics for research which interested readers can take up. As this field is emerging at a rapid pace, the contents of this book will help the readers understand the modern concepts and applications of solar energy.