[en] Sputtering, the ejection of target material following bombardments by energetic ions, is an extremely important technological process. Sputtering is a particularly important technique for the surface analyst, since it is used for both quantitative analysis of impurity concentrations and determination of depth distributions of impurities. Because of the complexity of sputtering, many of its fundamental parameters are difficult to ascertain. The depth of origin of sputtered atoms is a fundamental parameter of the sputtering process which, until recently, has been the subject of considerable controversy. Fortunately, both experiments and theory have improved greatly in this area, allowing a consensus to be reached on this important parameter. This report describes and evaluates these critical experiments and theories. (Author)