The principles of stacking procedures are described and their properties are discussed, including the fundamentals of the behavior of zone boundaries and the consequences of the self-correcting properties of boundaries in moving boundary electrophoresis, isotachophoresis, and zone electrophoresis. Further, the diverse possibilities of stacking procedures and the unavoidable destacking are described, and several examples of practically applied stacking procedures are given, besides many references to applications. Some limitations in the use of stacking procedures are discussed. The paper is arranged in such a way that it can serve both as an introduction into the field and as a reference overview.