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Potassium niobate KNbO₃ is a lead-free perovskite and a promising candidate to replace lead-containing ferroelectrics related to PbTiO₃. In this study, we use atomistic computer simulation and transmission electron microscopy to investigate dislocations in KNbO₃, first to establish the relationship between their atomic-scale properties and the macroscopic mechanical behavior, and second to study their influence on the ferroelectric properties of the material. The easiest dislocation glide system is found to be <110> {(1) over bar 10} at all temperatures, independent from structural phase transformations. The mobility of dislocations and the evolution of the microstructure are measured from room temperature up to 1173 K. A sharp transition in the yield stress is found around 800 K, attributed to the additional activation of the <100> {010} glide system at high temperature. Atomistic simulations quantify the effect of dislocations on the ferroelectric polarization, and TEM observations give indication of the nucleation of domain walls at dislocation cores.