Estimating sources of sediment comprising the sediment yield from a watershed is recognized as a difficult but important step in planning means and measures for watershed protection and development. The paper refers to procedures for making such estimates and presents t h e results of studies on 113 watersheds in various parts of the country. Sheet erosion is clearly the dominant source of sediment in most of the watersheds cited and the opinion is advanced that this is generally the case in the more humid parts of the country. In the cases cited, however, the proportion of sediment yield derived from sheet erosion ranged from 11 to 100 pct of the total and the conclusion is reached that watersheds must be considered individually with respect to sources of sediment.