A theory of kinetic-diffusion-controlled adsorption of polymers onto planar substrates has been developed. Equations were derived to calculate (a) the rate constant for polymer adsorption, (b) the coefficient of diffusion, and (c) the activation energy of diffusion in the adsorbed layer by using kinetic adsorption data at different adsorbate concentrations. It is shown that the adsorption kinetics over a wide range of polymer concentrations may be described by using the following models : (I) a kinetic-controlled adsorption for short times; (II) a diffusion-kinetic-controlled adsorption for intermediate times; (III) a diffusion-controlled adsorption for long times. The existence of I, II, and III regimes of adsorption kinetics is verified by using the experimental data for the adsorption of water-soluble associative polymers onto a planar surface of titanium dioxide single crystal.