Energy is acting as wheels for the national development and its progress. Rapid industrialization, infrastructural growth, population increase and our expanding economy have stressed the need to acquire additional sources of energy. However, conventional energy reserves are finite and will only be available for a limited period and with steadily increasing price. The fossil fuel use is also linked to environmental problems particularly global warming and climate change. The challenges of the present energy scene offer us a window of opportunity in the form of renewable energy sources to reduce dependency on fossil fuels by expanding and diversifying our energy supply mix and shifting the development part towards sustainability as well as environment and social responsibility. To achieve this objective, the knowledge of basic and fundamentals of alternate energy technology is needed. In this context, this book presents a systematic collection of all aspects of renewable energy resources. This book has been written in seventeen chapters, each chapter being with basic definition, working principle, fundamental theory of the various renewable energy sources. The contents of book include seven major aspects of non-conventional energy sources such as solar energy, solar thermal energy technology and devices, solar photovoltaic technology, biomass production, utilization and management, gasification technology, wind energy and other renewable energy sources such as geothermal, ocean energy and fuel cell technology. Most of the information presented in this book reflects a basis to acquire the understanding of the non-conventional energy sources. In this book, fundamentals, design, present state of art and future prospective are illustrated through graphs, figures, tables, flowchart, equations etc to make subject clear and useful. It is hoped that this book will be useful as reference book and a text book for students pursuing courses in energy studies.