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Ferroelectric switching governs the functional properties of ferroelectric perovskites. It is widely accepted that this switching depends on domain nucleation and pinning and that these processes can be controlled by the defect structure. However, an atomistic picture of the influence of one important class of defects—dislocations—on ferroelectric switching is missing. This is an important gap in knowledge as dislocations cannot be avoided at interfaces and can also be engineered by plastic deformation at high temperatures. Using atomistic simulations, we show how the cores of ⟨100⟩ edge dislocations in BaTiO3 can either act as nucleation centers for ferroelectric switching or pin walls depending on the direction of the applied field. The coupling between the electric field and polarization is strongest when the field is applied parallel to the Burgers vector of the dislocation.