The progress of investigations concerning the Pieniny Klippen Belt in the last twenty years is discussed and the actual state of opinions about its evolution presented. This most complicated zone of the Western Carpathians is remarkable for the complete separation of the unknown Paleozoic-Triassic basement from the Jurassic-Cretaceous strata. A nappe pile from shallow-water as well as deep-water successions resulted from the first compression. More rigid Jurassic-Lower Cretaceous limestones were during the following transpression torn of in the lenses (klippen) amidst the plastic sediments of the Upper Cretaceous strata („envelope”). A critical analysis of 15 successions (and their varieties) discerned up till now in the Slovak segment is given and their mutual position within the ancient sedimentary area is discussed. The following problems remain open: the origin of the exotic material in the Cretaceous and Paleogene conglomerates, the existence of a transform possessing oceanic crust, the place of Haligovce, Nizna and Michalova Hora Successions in the sedimentary area, the presence of the Magura Successions (Grajcarek Unit) on the Slovak territory, the possible provenance and transport of the Manin, Drietoma and Kostolec Successions from the Central-Carpathians nappes.