This volume investigates the contemporary fauna that inhabit the Cuatro Cienegas Basin. Divided into 15 chapters, it addresses and describes their diversity, taxonomic and biogeogaphic affinities, and ecological characteristics. The Cuatro Cienegas Valley is a unique oasis in the south-central region of the State of Coahuila, part of the Sonoran Desert, in Mexico. Several clues, specially derived from the study of the microbiota, suggest a very ancient origin of the valley and its permanence through time. This condition had promoted a high level of endemism and led to unique interactions between the resident species.