A signature feature of self-organization in biology is that of phase transitions, the spontaneous emergence of one stable pattern from another pattern which loses stability at the region of transition. Nonequilibrium phase transitions signify a qualitative shift between patterns under the monotonic scaling of a control parameter, and hysterisis is maintained if the original pattern is not returned under reverse scaling. Variables which demonstrate these phenomena are usually termed order parameters since they characterize all stable states of a system comprised of (potentially) high-dimensional components in a low-dimensional space. The coordination between rhythmic limb movements is one such system which is suitably characterized by the order parameter relative phase i.e., the phase relation of one limb with respect to another (Kelso, 1981). Recently however, similar patterns have emerged in rhythmic movements of limbs between persons (Schmidt, Carello, & Turvey, 1990) and between unimanuallimb movements with a regularly occurring environmental event (Byblow, Chua, & Goodman, this volume).