In this groundbreaking monograph, the authors introduce a new global taxonomic system and analyze the evolutionary relationships among various groups within the order Lepidoptera, utilizing the functional-morphological characteristics of male genitalia for the first time. The nomenclature for the genital muscles of both males and females has been standardized, and the principles of their functioning are thoroughly examined. A hypothesis regarding the origin and evolution of genital appendages and their musculature is proposed. To support this, the authors studied the musculature and skeletal structure of the terminal segments of the abdomen in over 600 species from the majority of families within the Holarctic and South Asian faunas of the order. The classification of certain families has been detailed down to the rank of tribe and subfamily, with the positions of some lesser-known or significantly diverging families or subfamilies defined or revised. For the first time, a catalog of all species of Lepidoptera in the world fauna is presented, detailing the musculature, attachment features, and functioning of genital muscles. The monograph includes numerous illustrations of the skeletal and muscular structures of copulatory organs, phylogenetic diagrams, and essential literature reflecting these topics. This work serves as a valuable reference and educational resource for further research in the fields of systematics, comparative morphology, and phylogeny of Lepidoptera.