This book reviews and summarizes the studies on the fish diversity of Japan. It covers the present knowledge of ichthyofauna, habitat distribution, phylogeography, ecology, morphology, and conservation, as well as the history of ichthyology and fish collections in Japan. The book comprises five parts: I. Fish Diversity and Ichthyology of Japan, II. Habitat Distribution and Species Diversity, III. Diversity within Species: Phylogeographic Perspective on Japanese Fishes, IV. Morphological and Ecological Diversifications, and V. Conservation of Fish Diversity in Japan.