Since the apparent stiffness due to contact of one surface on another relates directly to the localized resonant frequencies, it is believed that accurate account of this property will lead to the fundamental understanding of causes of friction-induced vibration and noise. The mathematical model of contact is utilized to develop formulae for normal and tangential contact stiffness. The inclusion of a study in which the various modes of elastic deflections of an asperity are also considered, as well as their effects. The bending, shear and Hertz contact modes of elastic deflection are assumed to simultaneously occur for an asperity. Investigation of the combined effect of bending, shear and Hertzian contributions to the contact stiffness is indicating that the equivalent contact stiffness is best represented, among the three types of stiffness, by that due to Hertzian contact.