Sample stacking is a tool that is in daily use in electrophoresis in order to enhance the efficiency and sensitivity of analyses. The application of sample stacking is described by numerous diverse practical procedures and numerous different names. This contribution shows that the present intricate situation is a heritage of the history where chromatographic and isotachophoretic approaches have been applied more or less independently. Further, this contribution shows that a unified view is possible and a general approach based on a frame with moving self-sharpening boundary may provide the required fundamental theory and criteria needed for successful application of sample stacking. Finally, the prospects of sample stacking are discussed.