Book excerpt: Given the backdrop of intense interest and widespread discussion on the prospects of a hydrogen energy economy, this book aims to provide an authoritative and up-to-date scientific account of hydrogen generation using solar energy and renewable sources such as water. While the technological and economic aspects of solar hydrogen generation are evolving, the scientific principles underlying various solar-assisted water splitting schemes already have a firm footing. This book aims to expose a broad-based audience to these principles. This book spans the disciplines of solar energy conversion, electrochemistry, photochemistry, photoelectrochemistry, materials chemistry, device physics/engineering, and biology.