An apparatus has been constructed to introduce known amounts of slip between a belt of an insulating material and a rotating, grounded metal roller over which the belt passes. This slip results in frictional generation of electrostatic charge on the belt. The charge generated has been measured at different belt speeds, tensions, angles of wrap of belt around the roller, and at various amounts of slip on the roller. The charge generated per unit area on the belt is correlated with the work per unit area done against the force of friction. A method is presented for obtaining a value of the coefficient of sliding friction between the belt and the roller by the measurement of the charge generated. In addition, evidence of increased charge transfer as a result of frictional heating is discussed.