A critical analysis of the geometric properties of oceanic fracture zones leads to the conclusion that their identification with ridge-ridge transform faults is an oversimplification. Models are presented, and examples are given, of processes (asymmetric spreading and differential spreading) which can alter the ridge-fracture zone pattern and extend active shear within lithospheric plates. These processes have a number of interesting tectonic consequences and could offer an explanation for, among other things, belts of intra-plate seismic activity and reversal of slip directions along a strike-slip fault.