Plate tectonics as a theory distinct from, yet embracing, continental drift and sea floor spreading was formulated by Wilson [1965] when he described a continuous network of ridges, transforms, and subduction zones bounding large rigid plates. Wilson explicitly discussed many of the consequences of the relative motion of torsionally rigid plates such as the changing geometry of certain kinds of transform linkage between ridges and subduction zones, evolving mosaics of ridges, transforms, and subduction zones, and the changing area of plates. At about the same time, Bullard et al. [1965] made the implicit assumption of torsional rigidity in using finite difference rotation poles to fit together margins of the continents bordering the Atlantic Ocean. An earlier, little publicized naturally occurring example of rigid body rotation, although it is on a flat surface and therefore allows translation, is provided by Stanley's [1955] study of tracks on Racetrack Playa, California. Stanley showed that parallel and concentric stone tracks resulted from stones embedded in and protruding from the base of wind‐blown rigid ice floes. McKenzie and Parker [1967], using the relative motion of the North American and Pacific plates, outlined for the first time the theory and consequences of relative plate motion on a spherical surface by using vector circuits to describe the instantaneous behavior of triple junctions (a technique later fully developed by McKenzie and Morgan [1969] and instantaneous angular velocities about the rotation axes between three plates. In particular, they showed how triaxial strain fields derived from first‐motion studies may be used as a rough guide to relative plate motion and applied the useful practice of drawing Mercator maps about instantaneous rotation poles that describe relative motion between two plates. In the following year, Le Pichon [1968] and Morgan [1968] developed comprehensive models of instantaneous global plate kinematics, and Isacks et al. [1968] showed how worldwide first‐motion solutions accorded in a systematic way with a set of torsionally rigid lithosphere plates in relative motion.