The performance and appearance of an electrophoretic display is strongly dependent on the stability of the colloidal suspension in the device. Two primary degradation modes in a suspension have been identified. One is classified as pigment agglomeration which is caused by an insufficient repulsive barrier between particles; the other is classified as pigment clustering which is caused by fluid motion within the cell. Both forms of instabilities are detrimental to the life of the display. The concept of colloid stability will be reviewed briefly and its relation to the image device will be discussed. The mechanism by which the suspension instabilities develop and the methods by which they can be eliminated will be described. Properly stabilized suspensions in a device have survived in excess of 2.5×108switches (15 600 h) with no serious signs of degradation.