In this book geological the conditions of speleogenesis in the Miocene gypsum in the Western Ukraine are characterized, particularly the role of lithological and structural prerequisites in speleogenesis. The special attention is given to structural and textural unhomogeneities in the gypsum stratum and to their role in the formation of fractures. Fracture systems in the gypsum and the structure of the unique maze cave systems are examined in details. It is shown that speleo-initiating fractures in the gypsum strata belong to the lithogenetic type and form largely independent multi-storey networks, with each storey being confined within a certain vertical structural/textural zone (unit) of the stratum. This determines the multi-storey structure of the caves in the region.