Displacement electrophoresis is a method of separating ions. After completion of this separation a qualitative and quantitative analysis of the sample composition can be made. In this report the separation process is investigated. It is shown that the sample introduces a transient system of homogeneous zones which are finally reduced to zones containing only one component of the sample. Starting from such basic equations as electroneutrality, current‐continuity, and conservation of ionic species, equations are derived which permit the calculation of all quantities of interest, such as local field strength, composition of a particular zone, and speed of zone boundaries. In the case of a two‐component sample the separation time can be calculated exactly; for the case of a multicomponent sample an approximate expression is given.