Magnetic, bathymetric, and seismic reflection data obtained aboard the M.V. RSA during the past 5 years provide new evidence for the evolution of the Mozambique basin in the southwest Indian Ocean. A major fracture zone, here identified with the Prince Edward fracture zone, has been traced over 2000 km from its active transform section across the southwest Indian Ocean ridge (SWIOR). Clearly lineated magnetic anomalies have been mapped and identified. The ridge itself, in the vicinity of the Prince Edward Islands, has been a spreading center since at least Cretaceous times. Spreading rates have varied considerably with two discontinuities which may be related to cessations in spreading or ridge axis jumps. A late Cretaceous change in spreading direction has resulted in opening (leaking) of transform faults and is the apparent cause of the complicated ridge axis morphology in this part of the Indian Ocean. Magnetic anomalies mapped within the Prince Edward fracture zone provide unique information on the process of adjustment to a spreading direction change. Fracture zone and magnetic anomaly trends in the Mozambique basin are different from those reported in the Madagascar basin and thus provide evidence for a plate boundary having existed between them.