This book is a compilation of eel research and fish migration studies for more than 40 years showing the research history and recent advances in eel studies. Dr. Katsumi Tsukamoto, the esteemed editor of this book, has been actively involved in eel research as one of the leading scientists in the world for a long time, and he and his team successfully collected the fertilized eggs and spawn-condition adult eels from the wild for the first time in the world. This book compiles the essentials of the scientific findings obtained by the editor and his colleagues and reviews the latest references of eel science. Knowledge and information in the book such as a spawning area survey, research on artificial production of glass eels, the discovery of a new species, etc. will attract the reader’s interest, as these are written based on the authors’ experiences. Readers can obtain a comprehensive understanding of eels from various aspects of eel science including the cultural and socio-economic importance of eels and valuable scientific information using state-of-the-art approaches. The book also endeavors to contribute to the conservation of eel species, some of which have been classified as endangered by the IUCN and to promoting harmonious coexistence between humans and nature.