The double-layer relaxation that can occur during the interaction of colloidal particles is described analytically. A dimensionless ratio alpha, which relates the characteristic approach time to the characteristic relaxation time, is identified. A solution for the electrical interaction force is presented for the case of two parallel hat plates approaching at a constant speed. An approximation based on Derjaguin’s approach is also provided for the case of two spheres approaching along the line of centers at constant speed, The results are compared with the traditional constant charge and constant potential limits of the electrical interaction energy. Critical values of ct for divergent electrical forces are identified for both examples.