The Mullins effect refers to the dissipation in cross‐linked rubber of mechanical energy in apparent excess of that due to linear relaxation processes or irreversible structural changes. Although it reflects nonaffine network motion in response to an applied deformation, contrary to previous assertions Mullins softening is found to be independent of the extent to which the junctions of the network are affinely displaced at elastic equilibrium. Rubbers of widely varying network structure were observed to exhibit comparable degrees of Mullins softening. Physically this softening arises from equilibration of local imbalances in the force along the network chains and from contraction of the primitive path of network chain ends. These mechanisms, which transpire too rapidly to be included in the linear relaxation spectrum, can be modeled empirically by the introduction of irreversibility into the damping function in the constitutive equation.