Subterranean fishes are found on every continent, in many different environments from shallow caves to deep phreatic groundwater. Over 125 species of obligate subterranean fishes (stygobites or stygobionts) are now known, and the rate of discovery is so high that there could be 250 known species by 2050. This book is the first comprehensive account of all known species since 1969. It includes an extensive introduction, including a complete systematic checklist, a history of investigations, a consideration of non-stygobitic fishes in caves, and a detailed analysis of the conservation status of these very rare animals. The main part of the book consists of an account for each species. Each species account contains details of systematics and taxonomy, distribution, habitat, other biological details, and a listing of all known publications on that species (example below). Details of these publications are given in the extensive bibliography which is the first attempt to list all publications on subterranean fishes. There are currently over 2000 publications in the list (example below). There are a number of appendices and the book is completed by an extensive “Note added in press” which contains information on species described and references published, during the final editing and production phase of the book.