Abstract: TERRESTRIAL life is an aqueous phenomenon. Although the physiological and ecological roles of water are of paramount importance in the lives of all organisms, ornithologists have paid little attention to the water requirements of birds, except inferentially with regard to distribution and habitat preferences. It is an interesting commentary on the fads and fashions of science that prior to World War II many hundreds of papers had been published on the food habits of birds, but only a handful of papers had given even semi-quantitative attention to the no less important problems of water economy. The inevitable preoccupation of government biologists with possible economic importances, together with the relatively simple technique of stomach analysis, early led to many studies of food habits. In contrast, water economy, while of basic biological significance, has no obvious economic implications, and its analysis requires the labor of maintaining live birds under controlled or semi-controlled conditions. During the past decade we have, together with various colleagues, undertaken a series of studies surveying the water economy of land birds in order to gain some preliminary insights into the ways different species have resolved the problem of maintaining a water balance. Although our studies have raised more questions than they have answered, they do allow the establishment of appropriate ecological and physiological perspectives. The purpose of this review is to sum up the conclusions from exploratory studies, in the hope that they may serve as a guide to more sophisticated physiological experiments and for more quantitative and precise ecological analyses. Our point of view is primarily ecological, and we shall confine our remarks to wild species of land birds. Readers interested in the domestic fowl should consult Sturkie (1954), and those requiring a broader physiological coverage should see Chew (1961). Historical summary.-Fewer than a dozen publications bearing specifically on the water economy of wild birds appeared prior to 1950. Buxton (1923) broached the problem of the water relations of desert-inhabiting birds and mammals, and suggested that some species might depend upon metabolic water. Allen's (1925) semipopular treatment of avian biology contains a brief section on drinking habits, and Stresemann (1927) in his monumental treatment of birds for the Handbuch der Zoologie noted the general lack of information on avian water economy. Apparently as a