Studies of bimanual coordination have found that only two stable relative phases (0 and 180 ) are produced when participants oscillate together two joints in different limbs. Increasing the frequency of oscillation causes an increase in relative phase variability in both phase modes. However, relative phasing at 180 is more variable than relative phasing at 0 and when the frequency of oscillation reaches a critical frequency a transition to 0 occurs. Because these results have been replicated in between people coordinations mediated by vision, we investigated the visual perception of relative phase. In Experiments 1 and 2, recordings of human interlimb oscillations exhibiting different frequencies, mean relative phases, and different amounts of phase variability were used to generate computer displays of spheres oscillating either side to side in a frontoparallel plane or in depth. Observers judged the coordination of the two spheres or the stability of their relative phase. Judgments mainly co-varied with mean relative phase and to a lesser extent with phase variability when the mean phase was near the values of 0 and 180 , even after extensive instruction and demonstration in Experiment 2. In Experiment 3, mean relative phase and phase variability were manipulated independently via simulations and observers were trained to perceive phase variability in testing sessions in which mean phase was held constant. The results of the first two experiments were replicated. The HKB model was fitted to mean judgment standard deviations.