Dynamic isoelectric focusing (IEF) is a new technique that is related to capillary IEF but uses additional high-voltage power supplies to provide control over the shape of the electric field within the capillary. Manipulation of the electric field changes the pH gradient, enabling both the location and width of the focused protein bands to be controlled. The proteins can be migrated to a designated sampling point while remaining focused, where they can be collected for further analysis. Traditional isoelectric theory for the prediction of band width and peak shape, however, does not hold up for very shallow electric field gradients like those encountered in dynamic IEF. The pH gradient along the capillary resembles a step gradient instead of the linear change as is often assumed. In addition, the concentration distribution of sample peaks is not Gaussian but rather a square band which has little overlap with neighboring peaks. These differences can lead to a better peak capacity for dynamic IEF than other IEF methods. The theory of dynamic IEF along with methods for the prediction of band width and peak shape will be presented.