This book presents the whole picture of the ecological and evolutionary study on the ground beetle group, the subgenus Ohomopterus of the genus Carabus, endemic to Japan. This flightless beetle group consists of many geographic races. They show divergence in key traits for reproductive isolation—body size and genital morphology, which leads to coexistence of two or more species. This beetle group provides an important material to study how a lineage of organisms diversify and form multi-species assemblage, and thereby multiply their species richness. The book introduces novel genomic approaches to resolve questions about evolution of Ohomopterus. The readers will find that this story of evolution in Carabus beetles revealed by recent approaches is much different from what was told in previous literature.Exploring different cases across a wide range of lineages is important in constructing a synthetic theory of species radiation and richness, includingspeciation and species coexistence. This study on Ohomopterus beetles contributes to the ongoing discussion to understand how and why species multiply and how species richness increases in one area of our planet.