Expressions are presented for the rate of strain relaxation, misfit dislocation nucleation, and propagation in strained Si1−xGex/(100)Si heterostructures. Independent measurements of misfit dislocation nucleation and 60° type a/2 〈110〉 dislocation glide velocity in the temperature range 450–1000 °C have led to a model which characterizes the kinetics of strain relaxation for 0<x<0.25. The generalized force or effective stress τeff, which drives strain relaxation, is defined for an arbitrary strain profile and strained‐layer geometry. New experimental data for misfit dislocation glide velocity (V in cm s−1) have been fitted to a semi‐empirical relation found to be appropriate for all Si1−xGex/(100)Si heterostructures, V=(4±2)⋅1013(τeff /μ)2 exp−[(2.25±0.05)/kT]. An analogous expression for the nucleation rate of new misfit dislocation segments was determined from experimental data, dN(t)/dt=BN0(τeff /μ)2.5 exp−[2.5±0.2)/kT], where N0 is the density of heterogeneous nuclei and B is a material constant ∼1018 s−1 for Si1−xGex. These expressions are combined in a kinetic model which is then used to predict the rate of strain relaxation in Si1−xGex/Si heterostructures.