Control of the electrokinetic charge of fibers in papermaking has become a focal point of intrest because of the many economic benefits it can afford. Microelectrophoresis is the most suitable and most reliable technique now available for measuring the charge. Criticisms of the technique that were based on deviations from the mobility data obtained by mass transport analyzer are found invalid. Instrumentation problems in several authors' work are discussed. New experimental evidence is presented to stress the role of the surface charge and to reconfirm the fundamental relationship between the drainage and retention maxima and the zero charge condition of fibers. Data are included on furnishes that contain high levels of alum and cationic flocculant, where bridging plays an important role. The zero charge point identifies the condition where a give polymer furnish produces its maximum effect.