The present work focuses on a presentation of the important ecological features peculiar to the region of brackish water and the problems they pose. Part 1 deals with the ecology and Part II with the physiology of brackish water. The book discusses salinity as a factor in the distribution of animals and definitions in backish water, it describes brackish-water types (seas, lagoons, river mouths, pool, shores), organisms and their features as well as biotopes (phytal zone, sandy floors, unconsolidated sea floor, plankton).