Slab gel electrophoresis is still the predominant technique for the separation of proteins and nucleic acids. Capillary electrophoresis, however, has potentially many advantages over the traditional slab gels and in the last few years there has been a steady transition from the slab to the capillary format. Early attempts to separate biological macromolecules were based on gel-filled capillaries, but soon it was discovered that the use of entangled polymer solutions offers several advantages over gels. It has now become possible to separate almost all species of macromolecules in such transient networks.