Thermal evolution modeling based on the geometry of the Scotian Basin, eastern Canada, and analysis of the shear resistance associated with lithospheric faulting are used to investigate the initiation of subduction at passive margins. Previous studies have demonstrated the difficulty of subduction initiation at mature passive margins. However, unique features along a passive margin may facilitate subduction initiation. Subduction may initiate along a part of the margin (1) by extensional or strike-slip deformation rather than shortening, (2) by deformation of the weaker continental lithosphere rather than oceanic lithosphere, (3) by heating and weakening of oceanic lithosphere due to lateral heat transfer from adjacent continental lithosphere, and (4) by heating and weakening of the lithosphere due to the passage of a mantle plume beneath the margin. The values of shear resistance under these conditions are still higher than those calculated for ridge push, indicating that subduction initiation at passive margins is difficult even with these weakening mechanisms. However, pulses of compression associated with plate reorganization may be enough to trigger subduction at such passive margins. ¿ American Geophysical Union 1993