Relative motion poles describing the displacement histories between the Pacific plate and once adjacent oceanic plates (Farallon, Kulla, Izanagi I, Izanagi II, and Phoenix) were derived for the late Mesozonic and Cenozoic eras. Because fracture zone and magnetic anomaly data are generally avaiable from the Pacific plate but not from adjacent plates, a new method of analysis for onesided data was required. This analysis produced stage poles and rates of relative plate motion and estimates of their confidence regions. The following are the main conclusions drawn from our analysis: (1) For time intervals of the order of 107 years, termed stages, relative motion ples for plate pairs remained nearly fixed. Between stages, shifts in poles were commonly both large and abrupt. Within stages, rates of plate motion were commonly observed to change markedly, indicating that plates changes speed more frequently than they changed direction. (2) The relative motions of all of the plates analyzed changed at about chron M11 (135 Ma), chron 34 (85 Ma), and chron 25 (56 Ma). (3) During the Early Cretaceous there were five oceanic plates in the Pacific basin rather than the four recognized by previous workers. (4) To determine the number of Farallon plates that existed to the east of the Pacific plate during the time interval from chron 34 (85 Ma) to chron 25 (56 Ma), fracture zones and magnetic anomalies that record Pacific-Farallon spreading from the northern, central, and southern Pacific plate were analyzed separately and collectively. The analysis shows that a single Pacific-Farallon relative motion pole and a single rate are consistent with all of the data. (5) Spreading rates along the Pacific-Kula ridge decreased markedly between chrons 32b and 25 (72-56 Ma), probably in response to the arrival of buoyant Kula lithosphere at a subduction zone northwest of the Bering Sea. (6) Soon after chron 25 (56 Ma), a major reorganization is recorded along the Pacific-Farallon boundary. The Kula-Farallon boundary is also thought to have charged during this reorganization. (7) Kula-Pacific anomalies north of anomaly 25 are modeled by assuming continued Kula-Pacific spreading after chron 25 (56 Ma). (8) Probably by chron 18 (43 Ma), Pacific-Kula spreading had ceased and the Kula-Farallon ridge system had evolved into alignment with the Pacific-Farallon spreading direction. However, the timing of these events is uncertain because Pacific-Kula data younger than chron 25 (56 Ma) are sparse.