Evaporation suppression in the reduction of evaporation by controlling the rate at which water vapor escapes from water surfaces. The need for water saving is greatest in areas of little rainfall and low runoff. Water losses by evaporation from storage reservoirs must be minimized for greatest utility of limited supplies. A review of the literature shows that evaporation can be retarded by either pysical or chemical means. It can be controlled by enclosure in a building, application of plastic covers, oil films, and monomolecular films. Monomolecular films hold the greatest promise for use on large areas of water such as reservoirs. From the litarature available it is apparent that these films introduce many chemical and physical problems. The suppressantsmust be nontoxic and odorless, especially if used on water-supply reservoirs. They should the free exchange of oxygen so that aquatic life is not endangered. The effects of water-borne bacteria on these films and the effects of the films on water of different qualities are not fully known. The physical problem of detecting the present of the film has not yet been solvet. Of the monomolecular films that have been investigated, the waxy alcohols such as hexadecanol and actadecanol show the greates promise.