The accelerating global drive for clean energy has substantially increased interest in electrolyser technologies, especially for producing green hydrogen at scale. Once considered niche industrial equipment, electrolysers are now pivotal emerging technologies within the decarbonised energy landscape. For more than a century since the first commercial alkaline water electrolyser was introduced, continuous research and innovation have fueled major technological advances, giving rise to new electrolyser designs that prioritise efficiency, durability, and scalability. This book captures these developments, detailing recent advances across six different technologies at various stages of maturity. Featuring up-to-date perspectives from international researchers and entrepreneurs, it addresses the prospects and challenges of each specific technology. It also examines how these innovations can facilitate the use of renewable electricity to convert feedstocks such as water and carbon dioxide into valuable fuels and chemical products, thereby advancing the global journey toward a cleaner, more resilient, and more equitable energy future. Spanning fundamental principles to practical, applied insights, the book is a valuable resource for both newcomers and experts seeking to understand the rapidly evolving field of electrolyser technologies and their potential to contribute to the clean energy transition.