A brief review is given of the historical development of power and power-factor measurements in balanced polyphase systems. Then follows the general theory of two distinct schemes for such measurements upon balanced systems having no neutral. One of these schemes is a generalization of the well-known indirect two-wattmeter sum-and-difference method, and the other is a direct scheme in which the active,P, and reactive,Q, powers are measured separately. The 2-phase systems are discussed briefly. A fairly comprehensive bibliography is given.