The book is based on a course that the author has taught for several years for biology students at Moscow University specializing in vertebrate zoology. Unlike foreign manuals of this type, the proposed book is built according to a slightly different plan: the first part is devoted to considering the relationship of fish with inorganic and organic environmental factors. The second part contains an overview of the main links in the life cycle of fish. Finally, the third provides a brief overview of the lifestyle of the main fishing groups.